Eugenie Martinez

Cu nanoparticles on 2D and 3D silica substrates: controlled size and density, and critical size in catalytic silicon nanowire growth

We report here the formation – via a bottom-up approach – of Cu nanoparticles supported on silica substrates as catalysts for the growth of silicon nanowires. The density and the size (3–5 nm) of Cu particles were controlled by exploiting the density and the distribution of surface silanols on both 3D silica nanoparticles and 2D silica thin films. The growth of Si nanowires on such Cu nanoparticles indicates that a critical particle size is needed for the fast growth of silicon nanowires.

Shallow heavily-doped n++ germanium by organo-antimony monolayer doping

Functionalization of Ge surfaces with the aim of incorporating specific dopant atoms to form high-quality junctions is of particular importance for the development of solid-state devices. In this study, we report the shallow doping of Ge wafers with a monolayer doping strategy that is based on the controlled grafting of Sb precursors and the subsequent diffusion of Sb into the wafer upon annealing. We also highlight the key role of citric acid in passivating the surface before its reaction with the Sb precursors and the benefit of a protective SiO2 overlayer that enables an efficient incorporation of Sb dopants with a concentration higher than 1020 cm-3. Microscopic four-point probe measurements and photoconductivity experiments show the full electrical activation of the Sb dopants, giving rise to the formation of an n++ Sb-doped layer and an enhanced local field-effect passivation at the surface of the Ge wafer.

Flatband Voltage Tuning of HfSiON-based Gate Stacks: Impact of High Temperature Activation Annealing and LaOx Capping Layers

INTRODUCTION The aggressive scaling of metal-oxide-semiconductor field-effects transistors (MOSFETS) faces the challenge of metal gate (MG) and high-k (HK) dielectric integration to reduce power consumption [1]. Hf-based oxides and silicates, such as HfSiON, are considered as the most promising candidates for next-generation gate dielectrics, owing to their high permittivity, with a sufficiently wide band gap and a good thermal stability [2]. However, the control of the threshold voltage (Vth) for the advanced nFET and pFET devices is challenging [3]. In gate first approach, the incorporation of LaOx capping layer has been reported to provide Vth shift towards the nFET band edge, yielding the necessary decrease of the effective work function (EWF) of the gate [4]. The mechanism of this voltage shift is attributed to La-induced dipoles at the HK/Si interface [5]. For this reason, the location of LaOx capping layer within the gate stack is a key factor for optimizing the transistor Vth. So far, detailed studies of La-capped gate systems have been focused on HfO2/SiO2 stacks. In this work, we have investigated the impact of high temperature thermal annealing and LaOx capping layer on electronic structure and band discontinuity for TiN/LaOx/HfSiON/SiON/Si gate stacks by coupling hard X-ray photoelectron spectroscopy (HAXPES) with synchrotron radiation and capacitance versus voltage (CV) measurements.

Effect of Nitridation for High-K Layers by ALCVDTM in Order to Decrease the Trapping in Non Volatile Memories

High-k materials have been introduced in non-volatiles memories for improving program/erase performance, reducing the applied voltage as well as avoiding degradation of the coupling ratio. Despite good program/erase performances, low data retention was also noticed, due to parasitic trapping . In order to reduce trapping effect on HighK insulator, thermal nitridation is investigated in this paper, the impact of nitrogen and its distribution on the structural properties of high-k layers. Various 6nm high-k films such as Al2O3, HfO2, and hafnium aluminates are deposited by ALD at 300°C with TMA, HfCl4 and H2O, in the equipment PULSAR 2000, using ALCVDTM (Atomic Layer Chemical Vapor Deposition). The (Hf:Al) cycle ratios used for hafnium aluminates deposition are respectively: (1:9), (1:6), (1:4), (1:3), (1:2) and (9:1), corresponding to hafnium concentration between 27 to 95%. HighK films are nitrided 30 min at 1.5 Torr under NH3 at 750°C. Film composition and structure are investigated by Angle Resolved X-ray Photo-electron Spectroscopy (AR-XPS), Auger Electron Spectroscopy (AES), Fourier Transform Infrared spectroscopy in Attenuated Total Reflection mode (ATR-FTIR), and Vacuum UltraViolet Spectroscopic Ellipsometry (VUV-SE). Al2O3 Auger profiles evidence traces of nitrogen (< 5 at. %) in the alumina film (Fig. 1). The nitrogen concentration is nearly uniform on the whole layer analyzed. ATR spectra display Al-O-N bonds (detected at 920-940cm) in nitrided amorphous alumina. Moreover, Si-O band intensity increases due to interfacial oxide regrowth. HfO2 On the contrary of Al2O3, nitrogen is segregated at the interface with the substrate, providing Si-N bonds evidenced by ATR. Then nitrogen species migrate to the HfO2/SiO2 interface. Crystallization of HfO2 appears after NH3 anneal at 750°C and after N2 anneal at 750°C but it was shown that N incorporation limits the crystallization. Hafnium aluminates Characterizations reveal different results for hafnium-rich and aluminium-rich alloys. Hafnium-rich HfAlO alloys Results for these nitrided layers are closed to nitrided HfO2 results. Auger measurements indeed show that nitrogen in hafnium-rich alloys is not present in the volume but migrates to the interface (Fig. 1). Nitrogen concentration at the interface can reach 20 at. %. XPS and FTIR-ATR evidence the same phenomenon. It was also shown that Hf-rich aluminates are amorphous asdeposited while nitrided ones are crystalline. Aluminium-rich HfAlO alloys Auger profiles show that nitrogen incorporation is possible in the volume for Al-rich HfAlO layers. The N concentration is lower than 5 at. % for a (1:9) Hf:Al ratio. It reaches a maximum of 16 at. % for a (1:2) Hf:Al ratio. The nitrogen concentration increases when the hafnium content increases in the HfAlO alloys (see arrow 1 in Fig.1). Afterwards, if hafnium concentration increases, then nitrogen disappears from the bulk of the alloy and migrates to the HfAlO/Si interface, as described in the hafnium-rich paragraph (see arrow 2 in Fig.1). XPS results were also used to investigate the nature of Nbonds. Hf-N bonds are detected for aluminium-rich alloys. When hafnium concentration increases, Al-N and Hf-N bonds are detected. The optical band-gap (accessed thanks to VUV-SE) decreases after nitridation (see arrow 1 in Fig.2). The decrease becomes stronger when the hafnium concentration increases. This band-gap decrease can be interpreted by an intrinsic modification of the alloy, our suggestion being the incorporation of nitrogen. Afterwards, the regime goes from aluminium-rich to hafnium-rich, as described by arrow 2 in fig. 2. TEM indicates that nitridation reduces the crystallization of Alrich hafnium aluminates (Fig.3). In summary, the impact of NH3 nitridation on high-k layers has been studied thanks to different techniques, such AR-XPS, AES, ATR-FTIR and VUV-SE. Similar behaviours for nitrided HfO2 layers and Hf-rich aluminates are obtained. Both have an absence of nitrogen in the volume of the layer and a segregation of nitrogen at the interface. For Al-rich aluminates, the proportion of incorporated nitrogen increases as the hafnium content increases. The maximum nitrogen incorporation (16 at. %) is reached for (1:2) Hf:Al ratio. A promising candidate for high-k layer in non-volatile memories is thus the (1:2) hafnium aluminate. It indeed stays mostly amorphous, and its volumic nitrogen concentration is the largest, which should help in decreasing trapping. Capacitors could demonstrate that such a trapping decrease is indeed associated to this composition. More details and results will be presented during the meeting.

Organic Mask Removal Assessment for 32nm Fully Depleted SOI Technology with TiN-metal Gate on HfO2

To pursue the device capability improvement, new materials have to be introduced in the gate stack. TiN metal gate on HfO2 is one of the solutions to replace existing gate. Thus, manufacturing processes, such as resist stripping, have to be adapted to these new materials as current processes can not be compatible. HfO2 compatibility was first studied by ellipsometry and ATR measurements, showing that Downstream type plasma (DS) with He-H2 or H2-N2 gas mix for dry processes, and Hydrozone ™ (HZ) for wet processes were fully compatible. Then TiN compatibility was investigated by WDXRF and XPS. Results indicate that the same processes as for HfO2 are compatible with TiN. Finally, effectiveness study proved that DS He-H2 or H2-N2 plasmas were similar to O2 plasma. To fully remove the polymers, HZ processes or derivatives have to be performed after plasmas.