Atomic layer etching (ALE) can result from sequential, selflimiting thermal reactions. The reactions during thermal ALE are defined by fluorination followed by ligand exchange using metal precursors. The metal precursors introduce various ligands that may transfer during ligand exchange. If the transferred ligands produce stable and volatile metal products, then the metal products may leave the surface and produce etching. In this work, selectivity in thermal ALE was examined by exploring tin(II) acetylacetonate (Sn(acac) 2 ), trimethylaluminum (TMA), dimethylaluminum chloride (DMAC), and SiCl 4 as the metal precursors. These metal precursors provide acac, methyl, and chloride ligands for ligand exchange. HF-pyridine was employed as the fluorination reagent. Spectroscopic ellipsometry was used to measure the etch rates of Al 2 O 3 , HfO 2 , ZrO 2 , SiO 2 , Si 3 N 4 , and TiN thin films on silicon wafers. The spectroscopic ellipsometry measurements revealed that HfO 2 was etched by all of the metal precursors. Al 2 O 3 was etched by all of the metal precursors except SiCl 4 . ZrO 2 was etched by all of the metal precursors except TMA. In contrast, SiO 2 , Si 3 N 4 , and TiN were not etched by any of the metal precursors. These results can be explained by the stability and volatility of the possible reaction products. Temperature can also be used to obtain selective thermal ALE. The temperature dependence of ZrO 2 , HfO 2 , and Al 2 O 3 ALE was examined using SiCl 4 as the metal precursor. Higher temperatures can discriminate between the etching of ZrO 2 , HfO 2 , and Al 2 O 3 . The temperature dependence of Al 2 O 3 ALE was also examined using Sn(acac) 2 , TMA, and DMAC as the metal precursors. Sn(acac) 2 etched Al 2 O 3 at temperatures ≥150 °C. DMAC etched Al 2 O 3 at higher temperatures ≥225 °C. TMA etched Al 2 O 3 at even higher temperatures ≥250 °C. The combination of different metal precursors with various ligands and different temperatures can provide multiple pathways for selective thermal ALE.
Two-dimensional (2-D) metal dichalcogenides like molybdenum disulfide (MoS 2 ) may provide a pathway to high-mobility channel materials that are needed for beyondcomplementary metal-oxide-semiconductor (CMOS) devices. Controlling the thickness of these materials at the atomic level will be a key factor in the future development of MoS 2 devices. In this study, we propose a layer-by-layer removal of MoS 2 using the atomic layer etching (ALET) that is composed of the cyclic processing of chlorine (Cl)-radical adsorption and argon (Ar) + ion-beam desorption. MoS 2 etching was not observed with only the Clradical adsorption or low-energy (< 20 eV) Ar + ion-beam desorption steps; however, the use of sequential etching that is composed of the Cl-radical adsorption step and a subsequent Ar + ion-beam desorption step resulted in the complete etching of one monolayer MoS 2 . Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) indicated the removal of one monolayer MoS 2 with each ALET cycle; therefore, the number of MoS 2 layers could be precisely controlled by using this cyclical etch method. In addition, no noticeable damage or etch residue was observed on the exposed MoS 2 .
This paper reports the first demonstration of dual high-k and dual metal gate (DHDMG) CMOSFETs meeting the device targets of 45nm low stand-by power (LSTP) node. This novel scheme has several advantages over the previously reported dual metal gate integration, enabling the high-k and metal gate processes to be optimized separately for N and PMOSFETs in order to maximize performance gain and process controllability. The proposed gate stack integration results in a symmetric short channel V t of ~±0.45V with >80% high field mobility for both N and PMOSFETs and significantly lower gate leakage compared to poly/SiON stack.
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