Person:

Lou, Xiabing

In advanced microelectronics, precise design of liner and capping layers become critical, especially when it comes to the fabrication of Cu interconnects with dimensions lower than its mean free path. Herein, we demonstrate that direct-liquid-evaporation chemical vapor deposition (DLECVD) of Co is a promising method to make liner and capping layers for nanoscale Cu interconnects. DLE-CVD makes pure, smooth, nanocrystalline, and highly conformal Co films with highly controllable growth characteristics. This process allows full Co encapsulation of nanoscale Cu interconnects, thus stabilizing Cu against diffusion and electromigration. Electrical measurements and high-resolution elemental imaging studies show that the DLE-CVD Co encapsulation layer can improve the reliability and thermal stability of Cu interconnects. Also, with the high conductivity of Co, the DLE-CVD Co encapsulation layer have the potential to further decrease the power consumption of nanoscale Cu interconnects, paving the way for Cu interconnects with higher efficiency in future high-end microelectronics.

Abstract We have prepared two new CaII amidinates, which comprise a new class of ALD precursors. The syntheses proceed by a direct reaction between Ca metal and the amidine ligands in the presence of ammonia. Bis(N,N′‐diisopropylformamidinato)calcium(II) (1) and bis(N,N′‐diisopropylacetamidinato)calcium(II) (2) adopt dimeric structures in solution and in the solid state. X‐ray crystallography revealed asymmetry in one of the bridging ligands to afford the structure [(η2‐L)Ca(μ‐η2:η2‐L)(μ‐η2:η1‐L)Ca(η2‐L)]. These amidinate complexes showed unprecedentedly high volatility as compared to the widely employed and commercially available CaII precursor, [Ca3(tmhd)6]. In CaS ALD with 1 and H2S, the ALD window was approximately two times wider and lower in temperature by about 150 °C than previously reported with [Ca3(tmhd)6] and H2S. Complexes 1 and 2, with their excellent volatility and thermal stability (up to at least 350 °C), are the first homoleptic CaII amidinates suitable for use as ALD precursors.

Inversion-mode GaAs wave-shaped metal-oxide-semiconductor field-effect transistors (WaveFETs) are demonstrated using atomic-layer epitaxy of La2O3 as gate dielectric on (111)A nano-facets formed on a GaAs (100) substrate. The wave-shaped nano-facets, which are desirable for the device on-state and off-state performance, are realized by lithographic patterning and anisotropic wet etching with optimized geometry. A well-behaved 1 μm gate length GaAs WaveFET shows a maximum drain current of 64 mA/mm, a subthreshold swing of 135 mV/dec, and an ION/IOFF ratio of greater than 107.

Atomic Layer Deposition (ALD) was used to grow single-crystalline epitaxial layers of high-k dielectric oxides on semiconductors with remarkably few defects or traps at the interfaces. La2O3 on GaAs(111) produced record-breaking transistors with both n-and p-channels, and CMOS circuits entirely in GaAs, including inverters, logic circuits and 5-stage ring oscillators. More conventionally oriented GaAs(100) substrates with etched (111) slopes also produced working transistors. ALD also grew single-crystalline epitaxial La2O3 films on Ge(111), and (Ca, Mg)O films on GaN(0001) substrates with high-quality epitaxial interfaces. These processes can be run in commercial ALD reactors using precursors produced by the Dow Chemical Company.

Summary form only given. Recently, GaN-based high-electron-mobility-transistor (HEMT) has demonstrated its promise in high frequency, high power and low noise electronic devices. The lattice matched InAlN/GaN HEMT structure provides a higher 2D electron density than AlGaN/GaN due to a larger bandgap offset and minimized short-channel-effects due to its thinner barrier. However, because of its several-nm thin barrier, those devices usually suffer from high gate leakage and interface trap issues, the device off-state performance is degraded and thereby the off-state breakdown voltage is decreased. Therefore, finding a good method to reduce the gate leakage and interface trap density is of great importance to improve the device off-state performance. In this study, we use atomic layer epitaxial MgCaO as gate dielectric to fabricate sub-100nm InAlN/GaN MOSHEMTs with significantly improved maximum drain current, current on/off ratio and low subthreshold swing.

In this work, we report on a 3D device fabrication technology achieved by applying a novel anisotropic wet etching method. By aligning channel structures along different crystal orientations, high performance 3D InGaAs devices with different channel shapes such as fins, nanowires and waves have been demonstrated. With further optimizing off-state leakage path by barrier engineering, a record high ION/IOFF over 10(8) and minimum I OFF~3pA/um have been obtained from InGaAs FinFET device. Scaling metrics for InGaAs GAA MOSFETs and FinFETs are systematically studied with Lch from 800 nm down to 50 nm and WFin/WNW from 100 nm down to 20 nm which shows an excellent immunity to short channel effects.

We demonstrate for the first time that a singlecrystalline epitaxial MgxCa1−xO film can be deposited on gallium nitride (GaN) by atomic layer deposition (ALD). By adjusting the ratio between the amounts of Mg and Ca in the film, a lattice matched MgxCa1−xO/GaN(0001) interface can be achieved with low interfacial defect density. High-resolution X-ray diffraction (XRD) shows that the lattice parameter of this ternary oxide nearly obeys Vegard’s law. An atomically sharp interface from cross-sectional transmission electron microscopy (TEM) confirmed the high quality of the epitaxy.High-temperature capacitance−voltage characterization showed that the film with composition Mg0.25Ca0.75O has the lowest interfacial defect density. With this optimal oxide composition, a Mg0.25Ca0.75O/AlGaN/GaN metal−oxide −semiconductor high-electron-mobility (MOS-HEMT) device was fabricated. An ultrahigh on/off ratio of 1012 and a near ideal SS of 62 mV/dec were achieved with this device.

Atomic layer deposition (ALD) processes were developed for growing MgO and CaO on GaN substrates using a home-built ALD reactor with amidinate-based precursors. An optimal deposition condition was then determined to deposit pure MgxCa1–xO by tuning deposition temperature, achieving a high-quality film without carbon and hydroxyl contamination. Band offset analysis was conducted by X-ray photoelectron spectroscopy on MgxCa1–xO/GaN samples with various compositions. Mg0.25Ca0.75O/GaN demonstrated band alignments between defect-free and fully pinned, while other ratios showed near fully pinned alignments, which agree with the best electrical properties achieved in our previous studies. This result indicates that band offset analysis provides a good aid in understanding part of the electrical and interfacial properties for oxide/semiconductor structures.

Polycrystalline, partially epitaxial (Sc_2O_3) films were grown on AlGaN/GaN substrates by atomic layer deposition (ALD). With this ALD (Sc_2O_3) film as the insulator layer, the (Sc_2O_3)/AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors showed excellent electrical performance with a high I({on})/I({off}) ratio of over 10(^8) and a low subthreshold slope of 75 mV/dec. The UV/NH(_4)OH surface treatment on AlGaN/GaN prior to ALD was found to be critical for achieving these excellent figures. In addition, the (Sc_2O_3)dielectric is found to be negatively charged, which facilitates the enhancement-mode operation. While bare (Sc_2O_3) suffers from moisture degradation, depositing a moisture blocking layer of ALD (Al_2O_3) can effectively eliminate this effect.