Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) are of great interest for applications in nano-electronic devices. Their incorporation requires the deposition of nm-thin and continuous high-k dielectric layers on the 2D TMDs. Atomic layer deposition (ALD) of high-k dielectric layers is well established on Si surfaces: the importance of a high nucleation density for rapid layer closure is well known and the nucleation mechanisms have been thoroughly investigated. In contrast, the nucleation of ALD on 2D TMD surfaces is less well understood and a quantitative analysis of the deposition process is lacking. Therefore, in this work, we investigate the growth of Al₂O₃ (using Al(CH₃)₃/H₂O ALD) on MoS₂ whereby we attempt to provide a complete insight into the use of several complementary characterization techniques, including X-ray photo-electron spectroscopy, elastic recoil detection analysis, scanning electron microscopy, and time-of-flight secondary ion mass spectrometry. To reveal the inherent reactivity of MoS₂, we exclude the impact of surface contamination from a transfer process by direct Al₂O₃ deposition on synthetic MoS₂ layers obtained by a high temperature sulfurization process. It is shown that Al₂O₃ ALD on the MoS₂ surface is strongly inhibited at temperatures between 125°C and 300°C, with no growth occurring on MoS₂ crystal basal planes and selective nucleation only at line defects or grain boundaries at MoS₂ top surface. During further deposition, the as-formed Al₂O₃ nano-ribbons grow in both vertical and lateral directions. Eventually, a continuous Al₂O₃ film is obtained by lateral growth over the MoS₂ crystal basal plane, with the point of layer closure determined by the grain size at the MoS₂ top surface and the lateral growth rate. The created Al₂O₃/MoS₂ interface consists mainly of van der Waals interactions. The nucleation is improved by contributions of reversible adsorption on the MoS₂ basal planes by using low deposition temperature in combination with short purge times. While this results in a more two-dimensional growth, additional H and C impurities are incorporated in the Al₂O₃ layers. To conclude, our growth study reveals that the inherent reactivity of the MoS₂ basal plane for ALD is extremely low, and this confirms the need for functionalization methods of the TMD surface to enable ALD nucleation.

Perpendicularly magnetized MgO-based tunnel junctions are envisaged for future generation spin-torque transfer magnetoresistive random access memory devices. Achieving a high tunnel magneto resistance and preserving it together with the perpendicular magnetic anisotropy during BEOL CMOS processing are key challenges to overcome. The industry standard technique to deposit the CoFeB/MgO/CoFeB tunnel junctions is physical vapor deposition. In this letter, we report on the use of an ultrathin Mg layer as free layer cap to protect the CoFeB free layer from sputtering induced damage during the Ta electrode deposition. When Ta is deposited directly on CoFeB, a fraction of the surface of the CoFeB is sputtered even when Ta is deposited with very low deposition rates. When depositing a thin Mg layer prior to Ta deposition, the sputtering of CoFeB is prevented. The ultra-thin Mg layer is sputtered completely after Ta deposition. Therefore, the Mg acts as a sacrificial layer that protects the CoFeB from sputter-induced damage during the Ta deposition. The Ta-capped CoFeB free layer using the sacrificial Mg interlayer has significantly better electrical and magnetic properties than the equivalent stack without protective layer. We demonstrate a tunnel magneto resistance increase up to 30% in bottom pinned magnetic tunnel junctions and tunnel magneto resistance values of 160% at resistance area product of 5 Ω.μm². Moreover, the free layer maintains perpendicular magnetic anisotropy after 400 °C annealing.

We present in this paper the use of Gas Source Molecular Beam Epitaxy for the large-scale growth of transition metal dichalcogenides. Fiber-textured MoS₂ co-deposited thin films (down to 1 MLs) are grown on commercially 200 mm wafer size templates where MX₂ crystalline layers are achieved at temperatures ranging from RT to 550 °C. Raman Spectroscopy and photoluminescence measurements along with X-Ray Photoelectron Spectroscopy show that a low growth rate is essential for complete Mo sulfurization during MoS₂ co-deposition. Finally, cross-section Transmission Electron Microscopy investigations are discussed to highlight the influence of SiO₂ and Al₂O₃ used surfaces on MoS₂ deposition.

This work proves that blistering is the partial delamination of a thick enough Al ₂ O ₃ layer caused by gaseous desorption in the Al ₂ O ₃ layer upon thermal treatments above a critical temperature: the Al ₂ O ₃ layer acts as a gas barrier and bubble formation occurs. First, using an atmospheric pressure rapid thermal processor with an atmospheric pressure ionization mass spectrometry, desorbing species upon heating of Si/Al ₂ O ₃ samples are identified: evident desorption peaks are observed around 400 °C for all spectra. The spectrum for m/e = 18, an indication of H ₂ O, illustrates that gaseous desorption from Al ₂ O ₃ and from the Si substrate itself continues up to 600 °C and 700 °C, respectively. Also, it is shown that in the case of a 30 nm Al ₂ O ₃ layer, blistering starts at same annealing temperatures as gaseous desorption begins. In the case of a thin enough (<; 10 nm) Al ₂ O ₃ film, blistering does not show. To complete the proof, elastic recoil detection measurements clearly show that after annealing a thick Al ₂ O ₃ film above 400 °C the H content is higher near the c-Si interface as compared to the near surface. Fortunately, effective lifetime and capacitance voltage measurements show that 5 to 10 nm Al ₂ O ₃ layers can still be adequate passivation layers after being annealed in N ₂ environment at temperatures up to 500-700 °C: (i) interface trap densities (D _it ) can remain below 1×10 ¹¹ cm ^-2 and (ii) fixed charge densities (Q _f ) stay negative and in the order of -3×10 ¹² cm ^-2 Random local Al back surface field (BSF) solar cells, fabricated using a blistered film as rear surface passivation and no additional contact opening step, clearly show that random local BSFs are created upon firing of a blistered rear passivation layer covered by metal. Therefore, it is clear that blistering should be avoided, since it will reduce the overall rear surface passivation. The key to avoid blistering is using 5 to 10 nm Al ₂ O ₃ passivation layers and performing an annealing step prior to capping and co-firing. Al ₂ O ₃ /SiN _x passivated local Al BSF p-type Si solar cells are made using an out-gassing step with temperatures up to 700 °C. For these cells, the reduction in blistering and hence improvement in rear surface passivation is clearly reflected in the gain in average Voc as a function of out-gassing temperature.

Monolayer-Si-passivated Ge nFETs with high electron mobility (175 cm ² /Vs at Ns=5×10 ¹² cm ^-2 ) and superior PBTI reliability (max. V _ov = |V _g -V _th | of 0.28V at 125°C) at 0.95-nm-EOT are demonstrated on a 300 mm Si wafer platform. The electron mobility is increased by optimizing the Si thickness while significant improvement in PBTI reliability is realized by band engineering using La-induced interface dipole and defect passivation using laser annealing. This is a significant step forward for the introduction of Ge nFET as high mobility device in advanced technology nodes.