M. Barozzi

Arsenic uphill diffusion during shallow junction formation

The behavior during annealing of low-energy As-implanted Si have been investigated by comparing secondary ion mass spectrometry (SIMS) and simulated profiles. Z-contrast scanning transmission electron microscopy (STEM) imaging has also been used to determine the As local distribution in proximity of the sample surface. The implants have been performed with energies between 1 and 10keV both through a thermally grown 11nm thick oxide and without any oxide mask. SIMS and STEM profiles show, after short annealing at 800–1000°C, an As pileup in the first nanometers of the Si matrix in proximity of the SiO2∕Si interface. We demonstrate that this phenomenon can be explained with a “Fickian” standard diffusion by assuming the presence of unspecified “dopant traps” near the SiO2∕Si interface that cause a drastic reduction of the dopant able to diffuse inside the bulk. We have also verified that removing before annealing the superficial 4nm of Si does not eliminate the As pileup. Different mechanisms proposed in li...

Real-time observation and optimization of tungsten atomic layer deposition process cycle

In the search for a chemical sensing strategy to monitor atomic layer deposition (ALD) processes suitable for real-time application in wafer manufacturing, we have applied downstream mass spectrometry sampling to study process dynamics during ALD cycles for tungsten deposition from WF6 and SiH4. The ALD reactor has UHV cleanliness conditions and incorporated a minireactor chamber to simulate the small reaction volume anticipated for manufacturing tools to achieve adequate throughput. Mass spectrometry revealed essential surface reaction dynamics through real-time signals associated with by-product generation as well as reactant introduction and depletion for each ALD half-cycle. These were then used to optimize process cycle time and to study the effect of process recipe changes on film growth. The reaction by-products were clearly observed as H2 from SiH4 exposure and SiF4 from WF6 exposure. For each of the two half-cycles, rapid increase of by-product leds to steady-state adsorption/reaction conditions,...

Low temperature oxidation of SiC preamorphized by ion implantation

In this article, we investigate the thermal growth of SiO2 films on 6H-SiC preamorphized by Ar+ ion implantation. The experimental conditions to grow oxide layers on SiC with high oxidation rate and low temperature have been determined. Rutherford back scattering channeling, secondary ion mass spectrometry, and x-ray photoelectron spectroscopy analyses have been used to investigate the oxide characteristics and composition. During wet oxidation at 800 °C, a linear growth rate of about 0.7 nm/min has been found for layers as thick as 240 nm. The presence of a SiO2Cx transition region between a stoichiometric SiO2 layer and the SiC substrate has been evidenced. The thickness of this transition layer increases with the oxidation time up to reach 118 nm for 390 min.

D-SIMS and ToF-SIMS quantitative depth profiles comparison on ultra thin oxynitrides

Abstract To realise gate dielectrics in the present ULSI technology ultra thin oxynitrides are used. Nitrogen quantitative depth profiles are mandatory to characterise this material. Depth resolution is the key analytical parameter to obtain useful ultra thin oxides characterisation. To improve this resolution very low primary ion impact energy is required. In the present paper, we compare quantitative depth profiles carried out by dynamic-SIMS and ToF-SIMS, respectively. Dynamic-SIMS analyses have been performed using a Cameca 4-f and the new Cameca Sc-Ultra 300 instrument. Different impact energies and incidence angles were used in combination with MCs+ ion monitoring. The D-SIMS profiles at keV and sub keV primary beam impact energies, are discussed and compared with ToF-SIMS data obtained using a IONTOF IV instrument.

Optimization of secondary ion mass spectrometry ultra-shallow boron profiles using an oblique incidence O2+ beam

The features of ultra-shallow junctions indicated by 2001 International Roadmaps require challenging characteristics for secondary ion mass spectrometry (SIMS) instruments: an ultra high depth resolution, minimization of transient width before the steady state and the ability to manage high concentration quantification in the near surface region. In this article a new magnetic sector SIMS, the Cameca Sc-Ultra, has been evaluated in order to profile boron ultra shallow junctions. In this apparatus the use of normal incidence oxygen bombardment is precluded and the primary column allows for a ⩾60° nominal incidence angle. Several approaches varying analytical parameters as energy, incidence angle and oxygen flooding have been tested on boron delta layers samples. In this way a quantitative comparison of different analytical methodologies is possible and the better analytical approach is pointed out. Moreover, an in situ laser depth profile measurement tool has been tested and the advantages and limitation a...

Multiscale structured germanium nanoripples as templates for bioactive surfaces

Nanostructured germanium substrates are produced by gold ion implantation; they show periodic ripples of nanometer size, decorated on the top and partially on one side with a forest of curled nanowires that end with gold-rich nanoparticles. For the first time, through a novel two-step soft lithography transfer process, the multi-scale nanopatterns are replicated, with features well below 100 nm, on biocompatible 2-norbornene ethylene cyclic olefin copolymer substrates. Given the suitable aspect ratio of the nanoripples and the peculiarity of their multiscale structure, the final substrates are available for cell–material interaction studies that can shed light on the role of the hierarchy of nanostructured materials in controlling the large-scale cellular behavior on biocompatible scaffolds. This work also presents an original combination of numerical analyses of scanning force microscopy images, which allows an accurate quantitative description of the outputs of the two-step transfer process.

Multilayer silicon rich oxy-nitride films characterization by SIMS, VASE and AFM.

In this work secondary ion mass spectrometry (SIMS), variable angle spectroscopy ellipsometry (VASE) and atomic force microscopy (AFM) are used to investigate the structure, composition and morphology of multilayer SRON films. Three/four SRON sequential layers were deposited on silicon wafers by PECVD and silicon, nitrogen and oxygen content was varied by changing the N2O/SiH4 ratio. The total thickness of the resulting SRON stack is about 50nm. SIMS analyses of NCs+, OCs+, SiCs+, in MCs+ methodology are performed by a Cameca SC-ultra instrument. Depth profiles are obtained at 500eV of primary beam impact energy with sample rotation. An approximate method to obtain silicon concentration is used. Total layer thickness are obtained from both SIMS and VASE measurements. In addition, we compare the thickness of the single layers obtained from VASE with the SIMS depth profiles. A detailed analysis of films morphology is obtained by AFM. The SRON stack is sputtered by SIMS until a certain layer is exposed, which is then analyzed by AFM. The sputtered layers are then etched in HF solution to better resolve the exposed nano-crystals.

Silicon defects characterization for low temperature ion implantation and spike anneal processes

In the last years a lot of effort has been directed in order to reduce ion implantation damage, which can be detrimental for silicon device performances. Implantations dose rate and temperature were found to be two important factors to modulate residual damage left in silicon after anneal. In this work high dose rate, low temperature, high dose arsenic and boron implantations are compared to the corresponding low dose rate, room temperature processes in terms of silicon lattice defectiveness and dopant distribution, before and after anneal is performed. The considered implant processes are the one typically used to form a source/drain region in a CMOS process flow in the submicron technology node. A spike anneal process was applied to activate the dopant. Low temperature, high dose rate implantations have found to be effective in reducing silicon extended defects with a negligible effect on the profile of the activated dopant. Experimental set up, results and possible explanation will be reported and discussed in the paper.

Preparation and Characterization of Nanocrystals using Ellipsometry and X-ray Diffraction

Nanocrystalline semiconductors embedded in dielectric matrices are currently under investigation for use in Si-photonics and in memory devices. The aim of a joint research activity in the FP6-ANNA*) project (http://www.i3-anna.org) is to develop and improve metrologies for the measurement of nanocrystal properties.

2D Optical Gratings Based on Hexagonal Voids on Transparent Elastomeric Substrate

A chromatic vectorial strain sensor constituted by hexagonal voids on transparent elastomeric substrate has been successfully fabricated via soft colloidal lithography. Initially a highly ordered 1.6 microns polystyrene spheres monolayer colloidal crystal has been realized by wedge-shaped cell method and used as a suitable mold to replicate the periodic structure on a polydimethylsiloxane sheet. The replicated 2D array is characterized by high periodicity and regularity over a large area, as evidenced by morphological and optical properties obtained by means of SEM, absorption and reflectance spectroscopy. In particular, the optical features of the nanostructured elastomer have been investigated in respect to uniaxial deformation up to 10% of its initial length, demonstrating a linear, tunable and reversible response, with a sensitivity of 4.5 ± 0.1 nm/%. Finally, it has been demonstrated that the specific geometrical configuration allows determining simultaneously the vectorial strain-stress information in the x and y directions.