Thomas David

Isabelle Berbezier

Jean-Noël Aqua

Marco Abbarchi

Antoine Ronda

Nicolas Pons

Francis Domart

Pascal Costaganna

Gregory Uren

Luc Favre

New strategies for engineering tensile strained Si layers for novel N-type MOSFET

Keywords: strained silicon, epitaxy, relaxation, condensation, MOSFET, carrier mobility

We report a novel approach for engineering tensely strained Si layers on a relaxed Silicon Germanium On Insulator (SGOI) film using a combination of condensation, annealing and epitaxy in selected conditions well chosen based on elastic simulations. The study evidences the remarkable role of SiO2 buried oxide layer (BOX) on the elastic behavior of the system. We show that tensely strained Si can be engineered by using alternatively rigidity (at low temperature) and viscoelasticity (at high temperature) of the SiO2 substrate. In these conditions, we get a Si strained layer perfectly flat and free of defects on top of relaxed Si1-xGex. We found very specific annealing conditions to relax SGOI while keeping an homogeneous Ge concentration and an excellent thickness uniformity resulting from the viscoelasticity of SiO2 at this temperature, which would allow layer by layer matter redistribution.

Remarkably, Si layer epitaxially grown on relaxed SGOI remains fully strained with -0.85 % tensile strain. The absence of strain sharing (between Si1-xGex and Si) is explained by the rigidity of the Si1-xGex/BOX interface at low temperature. Elastic simulations of the real system show that, due to the very specific elastic characteristics of SiO2, there are unique experimental conditions that both relax Si1-xGex and keep Si strained. Various epitaxial processes could be revisited in the light of these new results. The generic and simple process implemented here meets all the requirements of the microelectronics industry and should be rapidly integrated in the fabrication lines of large multifinger 2.5 V n-type MOSFET on SOI used for RF-switches applications and for many other applications.

Introduction

Strain engineering has long been an active area of development to enhance the key characteristics of Si MOS devices. There have been generally two different approaches. The first is a global or wafer scale pursued by IBM and then at Bell Labs to create a Si1-xGex template from which a strained layer could be formed. As a consequence of the lattice misfit, defect management and complexity were difficult challenges to overcome. Industrialization was not realized. On the other hand, alternative approaches for planar MOS architectures included a tensile strained contact etch stop layer for NMOS.

For PMOS, the substitution of Si with strained Si1-xGex alloys within the source/drain regions has been widely adopted. Within the era of digital scaling, the minimum devices are extensively used to construct the basic building blocks of digital design. The aforementioned approaches are most effective with minimum geometries. Challenging notwithstanding, the wafer scale engineering retains the advantage that the benefit of the mobility enhancement can also be realized also with longer channel lengths (>150 nm). In one particular application of interest and the motivation for this study, RF switches constructed of cascaded NMOS in RF-SOI technologies could benefit from a reduction of the on-state resistance without significant compromise of power handling. The commonly used figure of merit for RF Switches is Ron × Coff (fs). Ron (Ω) is an indicator of the insertion loss of the RF signal between the antenna and the desired port and Coff (fF) is an indicator of the isolation between antenna and undesired ports. Both have to be as low as possible. The Ron is mainly limited by the channel resistance, thus one way to reduce it is to decrease the Gate length, but this approach is limited because the device has to sustain high power especially in OFF-state. The process developed in this study aims at highly improving the mobility whatever the channel length, and thus decreasing the Ron accordingly.

Tensile strained silicon has been proposed for more than twenty years as a booster of silicon-based CMOS transistors to improve the performance of very large scale integrated (VLSI) circuits independent of device geometry and scaling. It has been experimentally demonstrated that the effective electron mobility in MOS structures can be significantly enhanced using tensile strained-Si channel grown on Si1-xGex relaxed buffer layer with an increase of Ion/Ioff ratio and more than 50 % transconductance enhancement in short-channel n-MOSFETs [START_REF] Samavedam | Novel Dislocation Structure and Surface Morphology Effects in Relaxed Ge/Si-Ge(graded)/Si Structures[END_REF]; [START_REF] O'neill | SiGe Virtual Substrate N-Channel Heterojunction MOSFETs[END_REF]; [START_REF] Mizuno | Electron and Hole Mobility Enhancement in Strained-Si MOSFET's on SiGe-On-Insulator Substrates Fabricated by SIMOX Technology[END_REF]; [START_REF] Rim | Fabrication and Analysis of Deep Submicron Strained-Si N-MOSFET's[END_REF]; [START_REF] Thompson | A 90 nm Logic Technology Featuring 50 nm Strained Silicon Channel Transistors, 7 Layers of Cu Interconnects, Low k ILD, and 1 /spl mu/m/sup 2/ SRAM Cell[END_REF]; [START_REF] Goo | Scalability of Strained-Si nMOSFETs Down to 25 nm Gate Length[END_REF]; [START_REF] Olsen | Evaluation of Strained Si/SiGe Material for High Performance CMOS[END_REF]; [START_REF] Sugii | Performance Enhancement of Strained-Si MOSFETs Fabricated on a Chemical-Mechanical-Polished SiGe Substrate[END_REF]. nchannel with mobility 75 % higher than in coprocessed bulk Si devices were reported, demonstrating that the mobility enhancement in strained-Si inversion layers was independent of vertical electric field. Furthermore, it was shown that the enhancement in carrier mobility observed at low lateral field did translate into improved performance at high lateral field [START_REF] Rim | Transconductance Enhancement in Deep Submicron Strained Si n-MOSFETs[END_REF]. In parallel, various theoretical calculations also predicted an enhancement of the drive current and then of the speed [START_REF] Ungersboeck | The Effect of General Strain on the Band Structure and Electron Mobility of Silicon[END_REF] [START_REF] Reiche | Strained Silicon Devices[END_REF] [START_REF] Flachowsky | Understanding Strain-Induced Drive-Current Enhancement in Strained-Silicon n-MOSFET and p-MOSFET[END_REF]. The strain of the Si layer was shown to cause an increase in the electron mobility (up to factors of 1.5 and 1.9 for x = 10 % and 20 % respectively), over the entire range of transverse electric field (E ⊥ ).

Among the first works dedicated to strained silicon, [START_REF] Fernandez | Two Dimensional Electron Gases in SiGe/Si Heterostructures Grown by Gas Source Molecular Beam Epitaxy[END_REF] aimed at the fabrication of two-dimensional electron gas (2DGs) consisting of a strained Si well sandwiched between two Si1-xGex relaxed layers and taking advantage of the 4.2 % misfit between Si and Ge crystalline lattice. Higher electron mobility was assumed to originate from changes in the band structure with carrier confinement in the Si layer.

The biaxial tensile strain introduces splitting of degenerate bands, which results in smaller in-plane conduction mass and reduced intervalley scattering thereby yielding improved carrier velocity [START_REF] Abstreiter | Strain-Induced Two-Dimensional Electron Gas in Selectively Doped Si/SixGe1-x Superlattices[END_REF].

While an optimization of the structures could be achieved with an increase of the space thickness and lowering the carrier concentration and the background impurities, the main bottlenecks to be raised concern the large density of threading dislocations throughout the whole structure.

Most of the work carried out in the 2000s has been completed on Si1-xGex relaxed substrate, trying to decrease the density of dislocations in the buffer and optimizing the associated surface roughness [START_REF] Berbezier | Elastic Strain Relaxation in Si1-xGex Layers Epitaxially Grown on Si Substrates[END_REF]; [START_REF] Gallas | Influence of Misfit and Threading Dislocations on the Surface Morphology of SiGe Graded-Layers[END_REF]; [START_REF] Perova | Composition and Strain in Thin Si1-xGex Virtual Substrates Measured by Micro-Raman Spectroscopy and X-ray Diffraction[END_REF]; [START_REF] Bauer | Relaxed SiGe Buffers with Thicknesses Below 0.1 μm[END_REF]; [START_REF] Fitzgerald | Dislocation Dynamics in Relaxed Graded Composition Semiconductors[END_REF]; [START_REF] Currie | Controlling Threading Dislocation Densities in Ge on Si using Graded SiGe Layers and Chemical-Mechanical Polishing[END_REF]. When the low-defect density Si1-xGex relaxed buffers have been integrated

into FETs, they have demonstrated high electron mobility in strained-Si and high hole mobility in strained-Ge (and Ge-rich alloys). n-MOSFET which have a simple epitaxial structure and require low Ge concentrations in Si1-xGex relaxed buffer layers, represent the devices for which improvements of performances in short-channel devices are most important and best documented, with robust mobility and significant transconductance enhancements demonstrated on large scales [START_REF] Lee | Strained Si, SiGe, and Ge Channels for High-Mobility Metal-Oxide-Semiconductor Field-Effect Transistors[END_REF]. The incorporation of a Si1-xGex layer with a high Ge content was also shown to minimize the overall strain within the device and to produce optimized strained-Si/Si1-xGex channel with even higher electrical performance in terms of transconductance, field-effect mobility and on-state drain current enhanced by up to 170 % while excellent off-state leakage currents and subthreshold characteristics [START_REF] Olsen | High-Performance nMOSFETs Using a NovelStrained Si/SiGe CMOS Architecture[END_REF]; [START_REF] Sugii | Role of Si1-xGex Buffer Layer on Mobility Enhancement in a Strained-Si n-Channel Metal-Oxide-Semiconductor Field-Effect Transistor[END_REF]. This result was obtained without Chemical-Mechanical Polishing (CMP) step of the surface, while it is well-known that such process step is critical for transistor properties reliability [START_REF] Lee | Strained Si, SiGe, and Ge Channels for High-Mobility Metal-Oxide-Semiconductor Field-Effect Transistors[END_REF]. Despite all the promising results obtained in research groups, so far, no technology based on strainedsilicon could be transferred to production due to the unreliability of the process induced by the formation of misfit dislocations during the various subsequent steps of the process. In fact, published drive current Ion enhancements are at most 15 % -20 % for Lgate ≈ 100 nm. Then more attention should be devoted to the optimization of several parameters besides mobility and CMOS process for strained-Si. So far, the various approaches under progress produce considerable variations in device performances. While the quality of the strained-Si epitaxial layer is usually directly linked to the underlying Si1-xGex relaxed buffer layer (threading and misfit dislocations density and surface morphology), in manufacturing, many other criteria have to be checked, for example uniformity of Gecontent and Si thickness to ensure consistent transistor performances on large scale wafers. But also, the level of Ge content in the Si1-xGex virtual substrate which is decisive for the electron mobility of n-MOSFET, since it sets the amount of strain-induced splitting between the 2 and 4 valleys in the Si layer.

It is therefore essential to study in detail the influence of the different conceptual parameters of the system under consideration. As regards Ge content, in some studies it was reported that the mobility monotonically increases with strain up to x ≈ 0.2 (strain 0.8 %) and then saturates. This is because at this strain level, the conduction-band splitting is sufficient to completely suppress intervalley phonon scattering, and thus only little enhancement of electron mobility could be gained at higher strain [START_REF] Kumar | Quantum Confinement Effects in Strained Silicon MOSFETs[END_REF].

In other studies, an enhancement of the electron mobility by ≈ 120 % was measured for x ≈ 0.30, despite the large misfit (between Si and Si1-xGex) causing high density dislocations. Monte Carlo simulations attributed these discrepancies to additional electron mobility-limiting mechanism such as defect scattering (surface roughness and high density of defects) in the epitaxial strained-Si/Si1-xGex system [START_REF] Kitagawa | Theory of Electron-Mobility Degradation Caused by Roughness with Long Correlation Length in Strained-Silicon Devices[END_REF]. Simulations results were confirmed by the comparison of mobilities measured on systems before and after CMP. It was shown that CMP eventually followed by epitaxy of thick silicon, significantly improves mobilities, when compared to devices without CMP [START_REF] Lee | Strained Si, SiGe, and Ge Channels for High-Mobility Metal-Oxide-Semiconductor Field-Effect Transistors[END_REF]. The thickness of the strained Si layer has also a strong influence: under low effective field, as this thickness decreases, the number of electrons in the Si1-xGex and close to the SiO2/Si interface increases, creating parasitic conduction and scattering events that degrade the overall mobility. Under high effective fields, the electrons are all located in the strained Si layer and the Si thickness has no influence on the mobility.

For NMOS devices the Si thickness should then be larger than ≈ 10 nm [START_REF] Aubry-Fortuna | Electron Effective Mobility in Strained Si/Si1-xGex MOS Devices using Monte Carlo Simulation[END_REF].

More recently, the combination of tensile strained silicon with Si1-xGex on insulator (SGOI) has been proven to offer new opportunities to increase the devices performances. New efforts were made to transfer the advantages obtained in bulk CMOS technology to insulating substrate [START_REF] Suh | Effects of Additional Oxidation After Ge Condensation on Electrical Properties of Germanium-On-Insulator p-Channel MOSFETs[END_REF]; [START_REF] Kim | Performance Assessment of Scaled Strained-Si Channel-On-Insulator (SSOI) CMOS[END_REF]; [START_REF] Langdo | Strained Si On Insulator Technology: From Materials to Devices[END_REF]; [START_REF] Boucaud | Photoluminescence of a Tensilely Strained Silicon Quantum Well on a Relaxed SiGe Buffer Layer[END_REF]; [START_REF] Tezuka | High-mobility strained SiGe-on-insulator pMOSFETs with Ge-rich surface channels fabricated by local condensation technique[END_REF]; [START_REF] Souriau | High Ge Content SGOI Substrates Obtained by the Ge Condensation Technique: A Template for Growth of Strained Epitaxial Ge[END_REF]; [START_REF] Jain | Tensile-Strained Germanium-On-Insulator Substrate Fabrication for Silicon-Compatible Optoelectronics[END_REF]. However, the measured values of ohmic mobilities that can be as high as 53105 cm 2 V -1 s -1 at low temperature, were shown to strongly depend on the interface roughness and on the material quality. In general, the mobility characteristics of n-MOSFETs fabricated on strained-Si layers transferred to insulating handle wafers has been found to be nearly identical to those on Si1-xGex graded buffers. The main reason for this is that generally, the fabrication process of the strained-Si/Si1-xGex relaxed buffer layer remains the same, while only a transfer step of Si1-xGex on SOI is added. Indeed, the tensile strained Si in the channel on BOX has been generally implemented following only two ways: 1) making strained Si/relaxed Si1-xGex on buried oxides using layer exfoliation to transfer the relaxed Si1-xGex buffer on SOI; 2) bonding and transfer the strained Si layer directly on the BOX.

Another method using SIMOX process was suggested but it is limited to x ≤ 0.1 which is then not useful for most of the microelectronic applications.

In this work based on elastic simulations we show that tensile strained Si can be engineered by alternatively using rigidity (at low temperature) and viscoelasticity (at high temperature) of the Si1-xGex/SiO2 interface. We then demonstrate both theoretically and experimentally an original and simplified process that should be easily integrated in NMOS device for the fabrication of tensile strained Si layer. We show that using a combination of epitaxy and condensation steps in very specific experimental conditions (i.e. low temperature Si1-xGex condensation and high temperature annealing) we can get strained Si layer perfectly flat and free of defects on top of relaxed Si1-xGex. In very specific annealing conditions Si1-xGex layer (on BOX) is relaxed, while keeping an homogeneous Ge concentration (x ≈ 20 %) and an excellent thickness uniformity. This results from the viscoelasticity of SiO2 at this temperature, which could allow layer by layer matter redistribution. Cross-section High Resolution Transmission Electron Microscopy (HRTEM) images highlight the very flat surface/interface and the absence of extended defects. Another very interesting result is that the Si layer grown on top of this relaxed Si1-xGex remains fully strained with -0.85 % tensile strain measured in the layer, by both geometrical phase analyses (GPA) of HRTEM images and interatomic lattice plane distance measurements. The absence of strain sharing (between Si1-xGex and Si) is explained by the rigidity of the Si1-xGex/BOX interface at low temperature (Si epitaxy at 500 °C). In more detail, the elastic nonlinear simulations of the real system in our experimental conditions show that for Si1-xGex (x = 0.2, e = 19 nm) the maximum thickness up to which there is no relaxation of the Si top layer is 83 nm.

Due to very specific elastic characteristics of SiO2, we have found unique experimental conditions that both relax Si1-xGex and keep Si strained. The generic process implemented here can be easily integrated in the fabrication lines of large multifinger 2.5 V n-type MOSFET on SOI used for RF-switches applications and meets all the requirements of the microelectronics industry for many other applications. The generic behavior found could be applied to many other heteroepitaxial systems.

Materials and methods

The process for the fabrication of tensile strained Si layer is schematically illustrated in Figure 1. The investigated SOI wafers are commercially available from SEH. The investigated structures were fabricated in state of the art 200 mm technology semiconductor facility of XFAB France. They initially consist of a 140 nm thick top-Si layer on top of 400 nm thick BOX (Figure 1a). The function of the poly-Si layer under the BOX is to suppress harmonic generation primarily from the active devices and to improve the linearity of RF switch devices. It is commonly referred to as a "trap-rich" layer. The 400 nm-thick BOX consolidates this effect and also provides isolation between back side and front side. The top Si layer is first locally thinned using LOCOS process followed by a wet etch to reach 20 nm. Thickness uniformity and surface flatness are systematically controlled over the entire wafer by ellipsometry. A thickness inhomogeneity lower than 8 % over the whole 8" wafer was found. At first, 20 nm Si1-xGex film with x = 0.15 is epitaxially grown by Solid Source Molecular Beam Epitaxy (MBE) in a 200 mm UHV growth chamber (SG800 model from DCA Instruments) after ex situ chemical cleaning and in situ thermal cleaning (Figure 1b) that consist of chemical oxidation (2 to 8 min HF etching) and thermal annealing (at 500 °C for 10 min) steps respectively. Si and Ge fluxes are produced with solid sources using e-beam evaporator and effusion Knudsen cell for Si and Ge respectively. The growth rates are monitored in situ by RHEED. Si and Ge growth rates are 1 nm min - 1 and 0.1 nm min -1 respectively. The growth temperature is set at 400 °C for both Si1-xGex and Si.

Next, thermal oxidation in O2 atmosphere is carried out in a Rapid Thermal Oxidation (RTO) furnace at low temperature (typically 750 °C). During this step the selective oxidation of only Si atoms, leads to the formation of SiO2 on the top of the structure and to the repulsion of Ge atoms underneath the SiO2, resulting in a pile-up of Ge at the SiO2/Si1-xGex interface (Figure 1c). Oxidation is carried out during 70 min to obtain a 10 nm thick Si1-xGex layer with a Ge concentration about 50 %. The wafer is then furnace annealed (Rapid Thermal Annealing) under inert nitrogen atmosphere. RTA of these samples were done at various temperatures and N2 pressures. This treatment promotes the interdiffusion between Si and Si1-xGex and leads to the homogenization of Ge concentration across the Si1-xGex/Si heterostructure (Figure 1d). As a result, Si1-xGex and Si layers mix to form a homogeneous Si1-xGex layer with a lower fraction of Ge and a total thickness thinner than the initial (Si1-xGex + Si) one. Small thickness is a key parameter to favor strain relaxation by gliding and redistribution of matter at the interface (see discussion). In addition, since the total amount of Ge in the SGOI layer is preserved throughout the process, the final Ge concentration in SGOI can be easily estimated ahead of time.

Condensation time is then fitted to obtain a final SGOI concentration of x  0.25 that is enough to efficiently stress the silicon top layer. It also has a sufficiently low thickness (< 20 nm) to avoid nucleation of dislocation and facilitate elastic strain relaxation (see simulations part) during the annealing step.

The last crucial step is the re-epitaxy of silicon. This is done after chemical etching of SiO2, i.e. by dipping the sample in a HF diluted solution (Figure 1e). A film of 70 nm Si is epitaxially grown in MBE at low temperature typically 500 °C (Figure 1f). The industrial developments require accurate and reliable metrology methods for the characterization and subsequent control of the magnitude of strain (relaxation) in the s-Si layer (Si1-xGex buffer) and the Ge content (x). To this end, Transmission Electron Microscopy (TEM), Energy Dispersive Spectroscopy (EDS) and Geometrical Phase Analysis (GPA) are the only analyses that give simultaneously and locally these parameters. Thickness and crystal quality of the SGOI layer were assessed by cross-section TEM. TEM specimens were prepared by Focused Ion Beam (FIB) milling using a dual-beam FEI Helios 600 NanoLab. The strain distribution throughout the films is imaged and mapped using GPA. High Resolution-TEM observations were performed using a Microscope MET FEI Titan 80-300 with Cs corrector operating at 300 keV. Transmission Electron Microscopy (TEM), Scanning Transmission Electron Microscopy and High-Angle Annular Dark-Field imaging (STEM HAADF) and Energy-Dispersive X-ray Spectroscopy (EDS) were done using a FEI Tecnai G2. Most of the strain values are given relatively to the reference (unstrained Si lattice from the substrate under the BOX). When the BOX is too thick, the reference is taken in the Si1-xGex layer whom Ge composition is estimated by EDS. More generally EDS using GATAN semi-quantitative analyses is used to estimate the Ge concentration throughout the films after the various fabrication stages.

Results and discussion

Strain determination

We start the process by the epitaxy of a Si1-xGex film with a low Ge concentration (x = 0.15) to avoid the formation of dislocation during the various fabrication stages. Epitaxial Si1-xGex layers with x ≥ 25 % could not be used because of the formation of dislocation during the process. Figure 2 Condensation is commonly carried out during dry thermal oxidation at high temperature (H.T.)

typically between 1000 °C and 1200 °C. However, during H.T. oxidation, dislocations nucleation is easily promoted [START_REF] Lin | Strain Evolution in SiGe-On-Insulator Fabricated by a Modified Germanium Condensation Technique with Gradually Reduced Condensation Temperature[END_REF]; [START_REF] Hutin | GeOI pMOSFETs Scaled Down to 30-nm Gate Length With Record Off-State Current[END_REF]; [START_REF] Boureau | Strain Evolution of SiGe-On-Insulator Obtained by the Ge-Condensation Technique[END_REF] together with the buckling of Si1-xGex layers due to the viscous flow of oxides surrounding the Si1-xGex layers [START_REF] Gunji | Strain Relaxation Mechanisms in Compressively Strained Thin SiGe-On-Insulator Films Grown by Selective Si Oxidation[END_REF]. We reported recently, that fully strained and free of dislocations Ge rich layers (GRL) with flat surface and abrupt interface, can be fabricated using low temperature condensation [START_REF] David | Kineticsand Energetics of Ge Condensation in SiGe Oxidation[END_REF]; [START_REF] David | Remarkable Strength Characteristics of Defect-Free SiGe/Si Heterostructures Obtained by Ge Condensation[END_REF]. In these experimental conditions, the basic mechanism of GRL formation is a self-limited interdiffusion process regulated by the entropic term of the formation energy which is minimum at Si0.5Ge0.5 at the expense of the elasticity driven interdiffusion. The process developed provides an easy and efficient way to produce planar GRLs with remarkable elastic features.

It also enables the total inhibition of the morphological instability (which commonly develops during the growth of Si1-xGex on Si [START_REF] Aqua | Growth and Self-Organization of SiGe Nanostructures[END_REF]; [START_REF] Berbezier | SiGe Nanostructures[END_REF]), together with the hindering of dislocations for critical thickness It should be noted that the annealing temperature was chosen to lie well below the solidus line of the Si-Ge alloy phase diagram, thereby avoiding the formation of dislocations. Higher temperature annealing, resulted in nucleation of dislocations, as already observed in previous studies [START_REF] An | Relaxed Gilicon-germanium-On-Insulator Substrates by Oxygen Implantation Into Pseudomorphic Silicon Germanium Silicon Heterostructure[END_REF]; [START_REF] Nakaharai | Characterization of 7-nm-Thick Strained Ge-On-Insulator Layer Fabricated by Ge-Condensation Technique[END_REF].

Fabrication of structures with partially relaxed layer free of defect were achieved for Si1-xGexOI with x = 0.15. For larger Ge concentrations, the layers were defective (formation of dislocations during annealing).

A critical step is the stress relaxation in the Si1-xGex layer upon annealing. To quantitatively map the 𝑐-lattice (𝑎-lattice) strain on both sides of the BOX, we use the High Resolution TEM image shown in Figure 5a. GPA is then performed to the image by applying the method described in [START_REF] Hytch | Quantitative Measurement of Displacement and Strain Fields From HREM Micrographs[END_REF]. We can note artefact values of strain close to the interface with the amorphous SiO2. They are related to the integration of pixels including both crystalline and amorphous cells in the analysis. Figure 6a shows the resulting color-coded map of ∆𝑐/𝑐 (∆𝑎/𝑎) in the 𝑎-𝑐 directions. The left part corresponds to the unstrained Si substrate (∆𝑐/𝑐 = ∆𝑎/𝑎 = 0 %). The right part features a deformation in the c-direction yy = + 1.5 % and a-planes xx = + 0.8 % with respect to Si (Figure 6b). These values correspond to partially relaxed Si1-xGex x = 0.23 as found by EDS. Unlike the sample before annealing, the distribution of the mechanical strain is constant across the layer. Importantly, while a partial relaxation is already obtained, there is no discontinuity (or defects) in the interfacial regions for ∆𝑐/𝑐 and ∆𝑎/𝑎, confirming the absence of misfit dislocations at the interface. This purely elastic relaxation is therefore the result of a sliding interface as already reported [START_REF] Boureau | Strain Evolution of SiGe-On-Insulator Obtained by the Ge-Condensation Technique[END_REF]. Overall, while GPA reveals a partial relaxation it also shows that 10 min annealing (950 °C) is not sufficient to achieve full relaxation (that would induce xx = 1 % and yy = 1 %) and not even the relaxation requested to significantly increase the electrons mobility. Several test samples were needed to validate the condensation/annealing method for forming a buffer as relaxed as possible (but without the nucleation of dislocations), the optimal annealing conditions found were: T = 970 °C, t = 30 min. The process generates an + 0.85 % relaxation of the Si1-xGex and ensures the absence of nucleation of dislocations during the subsequent steps.

These conditions are used on the XFAB pilot samples on the bench tests. On these samples, quantitative GPA of strain is made difficult due to the excessive thickness of the oxide which makes impossible to use the Si substrate as a reference (as a matter of fact, HR images cannot include in the same image both the top Si/Si1-xGex layers and the substrate). We then used Si1-xGex as a reference for GPA and the Ge concentration is deduced by EDS (x = 0.20 in these conditions).

A large-scale SEM image of the device where all the constituents of the system, including poly-silicon, BOX, Si1-xGex + Si and Pt cap layer are visible, is given in Figure 7a. The HR-TEM image of the square area evidences the perfect crystalline quality of the sample on large scale (Figure 7b). Even To get a complementary insight on strain relaxation, we counted directly on the image the atomic distances and integrated the measurements on areas typically 1000 × 1000 pixels. The (002) interplanar distances measured are 2.738 Å for Si1-xGex (x ≈ 0.2) which corresponds to a fully relaxed layer and 2.692 Å (instead of 2.715 Å for bulk Si) which corresponds to a tensile strain of -0.85 % in good agreement with the GPA measurements.

Simulations

The elastic theory is used to predict and explain the strain evolution of a Si film in epitaxy on Si1-xGex/SiO2 substrate (Figure 1f), as a function of experimental parameters (Si/Si1-xGex thicknesses and Ge concentration). We consider that during the epitaxy of Si, the Si1-xGex film is rigidly fixed at its lower interface to the BOX, so that this film is held in its initial strain state before Si epitaxy. In our experimental conditions, after low temperature condensation, we perform an annealing at 970 °C which homogenizes the Ge concentration throughout the (Si + Si1-xGex) layer. At this temperature, the viscous flow of the BOX provides an efficient elastic relaxation without dislocation nucleation. Consequently, in the simulations, we impose a displacement vector at the Si1-xGex/BOX interface which is zero with respect to the relaxed state. This condition introduces finite size effects compared to the semi-infinite layer where one imposes the displacement vector to be zero in the z → -∞ limit.

We note htot = h + e the total thickness, with h (e) the Si (Si1-xGex) thickness (Figure 1f). The Si free surface is located at z = H(r), where r = (x, y). We use the theory of linear and isotropic elasticity where the strain  and stress σ tensors are linearly related [START_REF] Landau | Theory of Elasticity[END_REF] thanks to the Young's modulus Y and Poisson's ratio ν that are supposed to be identical in the Si and Si1-xGex. Stress arises from the lattice mismatch between the film (Si) and the substrate (Si1-xGex), characterized by the misfit m = 1 -a f /a s , with a f(s) is the film (substrate) lattice parameter. In the following, we compute all strain vectors u with respect to a reference state defined with the substrate lattice parameter a s . Mechanical equilibrium enforces the relation ∇ • σ = 0 and the strain state is determined with the boundary conditions. The substrate lower surface is supposed to be rigid and is set at its relaxed lattice parameter, so that:

u(z = 0) = 0 (1)
This situation dramatically changes the strain state compared to the deposition on a crystalline softer or stronger substrate [START_REF] Berbezier | Accommodation of SiGe Strain on a Universally Compliant Porous Silicon Substrate[END_REF]; [START_REF] Aqua | Configurable Compliant Substrates for SiGe Nanomembrane Fabrication[END_REF]. As usual, the top surface is supposed to be free of stress, σ n(z = htot(r)) = 0, while the film/layer interface is coherent so that u (z = e -) = u (z = e + ) and

σ nz (z = e -) = σ • nz (z = e + )
In the case of a flat film, i.e. when H(r) = htot is constant, we find the solution:

𝑢 0 = (0,0, 𝑚 1+ 𝜈 1-𝜈 (𝑧 -𝑒))
in the Si film, while u0 vanishes in Si1-xGex . This solution is associated with an elastic energy density 𝜀 0 = 𝑌𝑚 2

1-𝜈

. Contrarily to the case where the lower layer surface is free of stress [START_REF] Mezaguer | When Finite-Size Effects Dictate the Growth Dynamics on Strained Freestanding Nanomembranes[END_REF],

in our current conditions, the flat film solution does not depend on the ratio e/htot, and there is no strain sharing between the film and the substrate.

When the film is modulated with a small corrugation, H(r) = htot + h1(r), the displacement vector may be expanded at first order in the surface slope [START_REF] Aqua | Nonlinear Evolution of a Morphological Instability in a Strained Epitaxial Film[END_REF] as u = u0 + u1 where u1 is conveniently found in Fourier space in the x and y directions, with a wave vector k. The solution of the mechanical equilibrium involves here both e kz and e -kz terms, both in Si and Si1-xGex layers. Eventually, one finds u1(k) and the elastic energy density on the surface  =  +  where 1 is given by

1(k) = -2(1 + ν) 0Ak(khtot)kh1(k) , (2)
k in Fourier space, with

𝐴 𝑘 (𝑥) = (3-4𝜈)𝑠ℎ(2𝑥)+2𝑥 (3-4𝜈)𝑐ℎ(2𝑥)+2𝑥 2 + 1 2 [1+ (3-4𝜈) 2 ] (3)
Note again that the finite size effects at first order depend here solely on htot. This result coincides with the large thickness limit htot → ∞ in the semi-infinite substrate case (large Si1-xGex thickness) [START_REF] Aqua | Influence of surface energy anisotropy on the dynamics of quantum dot growth[END_REF] where Ak = 1. More interestingly, it also corresponds to the s → ∞ limit of [START_REF] Aqua | Configurable Compliant Substrates for SiGe Nanomembrane Fabrication[END_REF] describing a film/substrate system deposited on a crystalline soft substrate with a Young modulus Y sub = sY. In our current situation (rigid interface) one finds that at low-k,

𝐴 𝑘 (𝑘ℎ 𝑡𝑜𝑡 ) = 𝑘ℎ 𝑡𝑜𝑡 1-𝜈 + 𝑂(𝑘ℎ 𝑡𝑜𝑡 ) (4)
Consequently, 1(k) is analytic and no longer singular as |k| in the k → 0 limit, contrarily to the usual elastic relaxation in the semi-infinite or soft cases. In particular, in the film/soft substrate (fss) case [START_REF] Berbezier | Accommodation of SiGe Strain on a Universally Compliant Porous Silicon Substrate[END_REF], [START_REF] Aqua | Configurable Compliant Substrates for SiGe Nanomembrane Fabrication[END_REF], one finds 𝐴 𝑘 𝑓𝑠𝑠 = 1/𝑠 + 𝑂(𝑘ℎ 𝑡𝑜𝑡 ) that only renormalizes the elastic energy density 1(k) by 1/s at low k•e elastic stress described by ( 2) may be relieved by the morphological evolution of the surface, as generically described by the Asaro-Tiller-Grinfeld instability [START_REF] Asaro | Interface morphology development during stress corrosion cracking: Part I. Via surface diffusion[END_REF], [START_REF] Grinfeld | Instability of the Interface Between a Nonhydrostatically Stressed Elastic Body and a Melt[END_REF]. Mass conservation enforces the diffusion equation [START_REF] Spencer | Morphological Instability in Epitaxially Strained Dislocation-Free Solid Films[END_REF] ∂h/∂t = D∆sµ where D is a diffusion constant, and ∆s, the surface Laplacian. The chemical potential µ is the sum of the elastic energy density and surface energy γ(h)κ, where γ(h) is the surface energy and κ = -(hxx + hyy) the surface mean curvature. The h-dependence of the surface energy describes the wetting effects [START_REF] Aqua | Nonlinear Evolution of a Morphological Instability in a Strained Epitaxial Film[END_REF]. In epitaxial systems, it may be given by γ(h)

= [γf 1 + cwe -h/δ w ] after inspection of atomistic results [START_REF] Lu | Towards Quantitative Understanding of and Stability of Ge Hut Islands on Si(001)[END_REF]. Given the solution for the elastic energy, one finds that a modulation of wave-vector k grows in the linear approximation as h1(k, t) = e ik•r+σt with

𝜎(𝑘, ℎ 𝑡𝑜𝑡 , ℎ) = - 𝑐 𝜔 𝛿 𝜔 2 𝑒 - ℎ 𝛿 𝜔 𝑘 2 + 𝐴 𝑘 (𝑘ℎ 𝑡𝑜𝑡 )𝑘 3 -𝑘 4 (5)
in units of the space and time scales l0 = γf /[2(1+ν)0] and t0 = l 4 /Dγf . Due to the presence of both the wetting and the finite-size elastic effects, the growth rate depends both on htot and h.

The first striking outcome of this analysis is that even without wetting interactions (cw = 0), the rigid substrate introduces a new critical thickness ℎ 𝑐 0 below which (h < ℎ 𝑐 0 ), σ(k) is negative and the instability is inhibited. Indeed, when cw = 0, the small-k expansion of σ is

𝜎 = -(1 - ℎ 𝑡𝑜𝑡 ℎ 𝑐 0 ) 𝑘 4 + 𝑂(𝑘 6 ) (6)
with

ℎ 𝑐 0 = 1 -𝜈 (7)
in dimensionless units. A similar result was found in [START_REF] Spencer | Morphological Instability in Epitaxially Strained Dislocation-Free Solid Films[END_REF] in the case of a rigid substrate. It is noticeable that ℎ 𝑐 0 only depends on a combination of elastic and surface effects and results from the lowering of the elastic relaxation due to the rigid interface [55]. In our experimental conditions, the interface rigidity weakens the instability development below a given thickness.

This inhibition is thence inferred to elastic relaxation inhibition (i.e. it is not the consequence of wetting interactions). Conversely, an increased softness promotes the instability as the elastic cost in a softer substrate (associated with the elastic relaxation) is lowered [START_REF] Berbezier | Accommodation of SiGe Strain on a Universally Compliant Porous Silicon Substrate[END_REF], [START_REF] Aqua | Configurable Compliant Substrates for SiGe Nanomembrane Fabrication[END_REF].

Another limit concerns the semi-infinite case where Si1-xGex is a very thick substrate (htot → +∞) while the Si film has a finite thickness (h). In these conditions, if we consider wetting interactions (cω ≠ 0), there is another critical thickness below which the morphological evolution cannot occur (when wetting interactions are sufficiently damped to allow strain In the general case, with both wetting interactions and a finite thickness htot, one finds a Stranski-Krastanov like behavior (Figure 8). Below the ℎ 𝑐 𝐴𝑇𝐺 critical thickness, that a priori depends on the layer thickness e, the growth rate is negative and the instability is inhibited (h1). The Si film remains fully strained and flat. Conversely, for h > ℎ 𝑐 𝐴𝑇𝐺 , the instability grows and strain relaxation spreads through the Si film (h3). ℎ 𝑐 𝐴𝑇𝐺 has two major specificities, first it depends only on e as a result of the combination of both the elastic inhibition and wetting interactions and second, its value is of the order of the instability length scale l0 which is of the order of hundreds of nanometers in our experimental conditions, well above the Si thickness (70 nm) deposited for the targeted device. The typical dependence of hc(e) is plotted in Figure 9. When e → +∞, htot also diverges and the instability growth rate coincides with the semi-infinite substrate case (hc(e) → ℎ 𝑐 𝐴𝑇𝐺 ). On the contrary, when e → 0, hc(e) nearly coincides with hc(e) ≈ h 0 -e. In between these two limits, ( 0 ≤ Ak ≤ 1 for ν ≤ ½) σ(k, htot, h) (and strain relaxation) is always much reduced compared with the normal ATG situation. In presence of wetting interactions, σ(k, htot, h) is even lower than without wetting interactions, and the instability only develops when htot ≥ h 0 with hc(e) ≥ h 0 -e which in our experimental conditions correspond to 83 nm (for x = 0.2 and e = 19 nm)

As a conclusion, the calculations show that strain relaxation will occur when hc(e) ≥ sup(ℎ 𝑐 𝐴𝑇𝐺 , h 0e). This condition is indeed satisfied in the numerical solution for hc(e) plotted in Figure 9.

Discussion

During this study we blew out crucial locks that were blocking the fabrication of Si. First the strain relaxation of Si1-xGex (SGOI) which must be achieved without change of the uniformity and flatness and without dislocation nucleation. In these layers, strain relaxation commonly occurs by the introduction of 60° perfect dislocations or planar defects, such as microtwins and stacking faults that are associated with loss of coherency during oxidation/annealing. In addition to this extended defect mechanism, the buckling of thin SGOI films has been demonstrated as another mechanism which explains the discrepancy between thermodynamically predicted strain levels and experimental results [START_REF] Gunji | Strain Relaxation Mechanisms in Compressively Strained Thin SiGe-On-Insulator Films Grown by Selective Si Oxidation[END_REF]. When the system is deposited on a SiO2 viscous layer, the buckling rate of the SGOI film (i.e. the inverse of the bucking time constant B) can be expressed using the Föppl von Kármán plate equation which describes the large deflection of thin compressed films with:

1 𝜏 𝐵 = 𝐸 12𝜂(1 -𝜂 2 ) [ 𝑠𝑖𝑛ℎ(2ℎ 𝑆𝑖𝑂 2 𝑘) -2ℎ 𝑆𝑖𝑂 2 𝑘 1 + 𝑐𝑜𝑠ℎ(2ℎ 𝑆𝑖𝑂 2 𝑘) + 2(ℎ 𝑆𝑖𝑂 2 𝑘) 2 ] × [12𝑒(1 -𝜈)𝑒𝑘 -(𝑒𝑘) 2 ]
where  is the viscosity of SiO2, ℎ 𝑆𝑖𝑂2 the thickness of SiO2 and k the wavenumber of a particular buckling mode [START_REF] Gunji | Strain Relaxation Mechanisms in Compressively Strained Thin SiGe-On-Insulator Films Grown by Selective Si Oxidation[END_REF]. In these conditions, the relaxation of SGOI strain, below the glass transition temperature (≈ 1100 °C) has the same activation energy as viscous flow and is controlled by the viscosity [START_REF] Doremus | Viscosity of Silica[END_REF] which varies with temperature following an Arrhenius relation. In our experimental conditions, after low temperature condensation (800 °C), Si1-xGex layer (x=0.4 and hSi1-xGex ≈ 12 nm) is fully strained on SOI (as already reported [38] [39]). The critical step is then to transform this fully strained Ge rich layer into relaxed SGOI (preferably fully relaxed). In addition, as deduced from the simulations, Si1-xGex should have low thickness and concentration to avoid elastic strain relaxation (since hc(e) and x are directly related). For the targeted device, the layer should also be homogeneous in concentration, flat (no buckling), and free of dislocation. The results show that at a very crucial temperature annealing (T ≈ 950 °C) both homogenizing of the concentration throughout (Si + Si1-xGex) and strain relaxation are optimal. It provides the fabrication of a perfectly flat Si1-xGex template layer with x = 0.23 % and e ≈ 20 nm. In addition, at this temperature (i.e. below the glass transition temperature), SiO2 has a low viscosity which could allow a slow layer by layer redistribution of Si1-xGex slightly pushing SiO2 in a planar way which would provide elastic strain relaxation without buckling [58]. The annealing is also very efficient to flatten the Si1-xGex/BOX interface. The temperature of annealing is here very crucial since at lower temperature, strain is not relaxed (SiO2 is too rigid) while at higher temperature, there is nucleation of dislocations.

The second tricky step is the epitaxy of Silicon which should lead to expitaxial Si, fully strained on Si1-xGex. As demonstrated by elastic theory, epitaxy should be performed at low enough temperature (500 °C) to have a rigid Si1-xGex/BOX interface and avoid strain sharing, as reported in the simulations. Indeed, strain sharing is forbidden only when the interface is rigid. It is roughly explained by the energy cost (when the interface becomes very rigid) to relax strain at this interface which becomes too large as compared to the gain of relaxation energy. In addition, the simulations also show that e should be lower than the critical thickness hc(e) where corrugation development starts as a consequence of Si strain relaxation (Figure 8). We have shown that it is the combination of all these very specific parameters chosen on the basis of elastic simulations that allow to get the fully strained Si layer as demonstrated here.

Conclusion

Thanks to a multi-disciplinary approach based on elastic modelling and series of highly specialized experiments, we have developed a simple process for engineering tensile strained Si layers on a relaxed SGOI film using parameters precisely fitted to theoretical predictions. Contrary to the previous processes reported in the literature, the present method allows to fabricate defectless

Figure 1 :

 1 Figure 1: Process flow diagram: (a) Nominal substrate after Si thinning; (b) Si1-xGex epitaxy; (c) Ge condensation during RTO; (d) Furnace annealing for homogenization (950 °C); (e) Chemical etching of oxide; (f) Si epitaxy

Figure 2 :

 2 Figure 2: STEM HAADF cross-section images of: (a) the whole structure; (b) The Si/Si1-xGex

Figure 3 :

 3 Figure 3: (a) EDS line profile of the elemental composition of the layers; (b) TEM diffraction

  much larger than the ones commonly obtained by direct deposition. Those behaviours were explained by the injection of self-interstitials in the GRL during condensation.The present process takes advantage of this fabrication of GRLs, fashioning them for the fabrication of relaxed Si1-xGex template layers with lower Ge concentration, best suited to the device targeted here.The first condensation tests were performed at 800 °C using a test sample constituted of 25 nm BOX and 19 nm Si1-xGex/SOI. The reduced thickness of the BOX allows for more reliable GPA strain measurements. A cross-section TEM image of the resulting structure is given in Figure4together with the EDS line profile. They both evidence the presence of an ultra-thin Si layer (4 nm) between the Si1-xGex and the BOX layers, remaining from the SOI layer. From previous studies, we know that this ultra-thin layer has strong interactions with the BOX and maintains the top layer fully strained. Ge concentration is about 40 % (lower than the 50 % concentration obtained at temperatures < 800 °C) and has a diffuse interface with the Si layer as already observed in[START_REF] David | Kineticsand Energetics of Ge Condensation in SiGe Oxidation[END_REF] [START_REF] David | Remarkable Strength Characteristics of Defect-Free SiGe/Si Heterostructures Obtained by Ge Condensation[END_REF]. There is no relaxation and no dislocations in the layers.

Figure 4 :Figure 5 :

 45 Figure 4: (a) TEM cross-section image of the structure after condensation at 800 °C; (b) Corresponding EDS line profile of Si, O and Ge.

Figure 6 :

 6 Figure 6: (a) Color scale map of c-planes (yy) and a-planes (xx); (b) Distribution of strain integrated on areas pointed by the red squares in (a).

  more interestingly are the color-coded GPA maps of the Si/Si1-xGex which evidence a constant strain from Si1-xGex to Si in the direction parallel to the surface and an abrupt change between Si1-xGex (set by calibration at yy = + 0 %) to the tensile strained Si (Figure7c). From this analysis (taking Si1-xGex as reference) we find a tensile deformation of the Si layer xx = 0 (∆𝑎/𝑎) and yy = -0.78 % (∆c/c), not so far from the expected fully relaxed value (yy = -1.1 %).

Figure 7 :

 7 Figure 7: (a) Large-scale TEM image of the cross-section sample on which one can see the constituents of the device, from bottom to top: Si substrate, poly-Si, BOX, Si/Si1-xGex and Pt cap layer; (b) HRTEM image of the Si/Si1-xGex/BOX system; (c) HRTEM reference image and GPA color-coded map of xx (∆𝑎/𝑎) and yy (∆c/c) in the 𝑎-𝑐-directions.

2 )

 2 relaxation). It corresponds to the ATG instability (ℎ 𝑐 𝐴𝑇𝐺 ) in presence of wetting where ℎ 𝑐 𝐴𝑇𝐺[START_REF] Aqua | Nonlinear Evolution of a Morphological Instability in a Strained Epitaxial Film[END_REF]. In these conditions, Ak = 1 and we find that below ℎ 𝑐 𝐴𝑇𝐺 , σ(k) is always negative, while above ℎ 𝑐 𝐴𝑇𝐺 , σ(k) displays a range of wave-vectors where it is positive, so that a morphological instability can grow.

Figure 8 :

 8 Figure 8: Growth rate of the elastic instability as a function of its wavevector k for a given layer thickness e and for h1 < 𝒉 𝒄 𝑨𝑻𝑮 (dashed blue line), h2 = 𝒉 𝒄 𝑨𝑻𝑮 (solid black line), h3 > 𝒉 𝒄 𝑨𝑻𝑮

Figure 9 :

 9 Figure 9: Numerical solution for hc(e) above which the instability grows, as a function of the

  layers thanks to a fine tuning of experimental parameters: Si1-xGex composition and thickness and temperatures of epitaxy, condensation and annealing. The three crucial steps are: (i) fabrication of ultra-thin Ge rich Si1-xGex layer by low temperature condensation, (ii) relaxation and homogenization of SOI/Ge rich Si1-xGex layer during annealing without dislocation nucleation nor buckling. Elastic relaxation results from the low BOX viscosity at high temperature, which would promote a slow layer by layer Si1-xGex matter redistribution (iii) Si epitaxy without strain sharing, producing defect-free, planar and fully strained Si. Elastic simulations show that inhibition of strain sharing is only made possible if Si1-xGex buffer layer is thin and rigidly fixed to the BOX. The process reliably and reproducibly produces a Si layer under -0.85 % tensile strain. According to the literature, such tensile strain should lead to 110 % increase of the electron mobility, and thus significantly decrease the Ron*Coff figure of merit of RF-switches. The developed process is applied to the pilot large multifinger 2.5 V n-type MOSFET on SOI used for RF-switches applications of XFAB. The electrical characteristics foreseen place it at the top level of the components made in the world. The developed process is simple and generic and can be adapted to many other devices.

J.N.A. developed the theoretical model and made the calculations. All authors contributed to the scientific discussions, manuscript preparation, and final revision. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. *Corresponding authors: isabelle.berbezier@im2np.fr; luc.favre@im2np.fr;

Funders L.F., M.A., A.R. and I.B. would like to thank Nanotecmat and CP2M platforms for providing elaboration and characterization equipments. T.D., N.P., F.D., P.C., and G.U. are grateful to NANO2022 for financial support.

Author Contributions


Keywords: CEA -Carrier: GLUT1 -… Radiopharmaceutical -Peptide -Antibody -NorA analog -Glucose -… Gamma: scint, SPECT/CT Béta +: PET, PET/CT Alpha, béta-, Auger e-: therapy

Imaging and molecular radiotherapies

Stacked-foil technique:

-Target/monitor/degrader pattern -Thin foils:

E loss small and constant -One cross section value per foil Activity and cross section:

σ = Act . A χ. Φ . 𝒩𝒩 A . ρ . e . (1 -e -λ.t ) σ = σ ′ . 𝜒𝜒 ′ .

Use of a Faraday cup:

- seven types of incidents particles (n, p, d, t, He-3, alpha-particle, gamma ray) all isotopes living more than 1 second (~ 2800 isotopes) all files are original except 15 (natural carbon from JENDL-4.0, 1,2,3 H, 2,3 He, 6,7 Li, 10,11 B, 9 Be, 14,15 N, 16

-

  : whole body 3D mapping of a biomarker, non invasive Multimodality: SPECT/CT, PET/CT then PET/MR In biology, new vectors: peptides, humanized antibodies, nanobodies … New radionuclides are needed to match with these new vectors A large set of radioisotopes with very different characteristics is suitable: -Radiation type for the different applications -Half-life -to match the bio-distribution time -Chemical properties -to attach to the vector molecule -Production yields -to get the purest product -Production capacities -to envisaged large scale Identify production route and define production process even large scale production (reactors, accelerators by spallation, fission or activation) -Identify and quantify contaminants -Define waste management process -Help scientists working in a pluridisciplinary team (nuclear physicists are use to do that) -Discuss with physicians to promote its use Over the last years, several radionuclides have emerged: -Béta+: Cu-64, Ga-68, Zr-89 … -Gamma: Sn-117m … -Béta-: Ho-166, Lu-177 … -Alpha: At-211, Bi-212, Bi-213, Ra-223, Ac-225 ... -Theranostic: Sc-44/Sc-47, Cu-64/Cu-67, Ga-68/Lu-177 … Terbium quadruplet Tb-149, 152, 155, 161 -Auger: Sn-117m, Tb-155 (at the research level for the moment)To do so, we possess facility (will possess) available for irradiations equipped with experimental techniques such as the stacked-foil technique

-

  Beam dump placed at the end of the stack to control the intensity during the irradiation HPGe coaxial detector γ spectra recorded on 8192 channels -Dead time: < 10% (sum peak) -FWHM:1.04 keV at 122 keV ( 57 Co) -Activity values: FitzPeaks 1.97 keV at 1332 keV ( 60 Co) -T 1/2 , E γ , I γ : Lund/LBNL, NNDC -Energy and efficiency calibrations: Co and Eu γ rays used to extract production cross section of 230,232,233 Pa Target and monitor:  counted twice  during > 24 hrs  2 week delay Head of the HPGe detector Novel therapeutic nuclide Th-232(p,3n)Pa-230 → U-230 U-230(21 d)/Th-226(31 min) α RIT for leukaemia treatment 4 α cascade of 27.7 MeV C. Duchemin et al., Phys. Med. Biol. 60 (2015) 931J. and Rochman D., Nucl. Data Sheets, 113, 2012 TALYS Code for the simulation of nuclear reactions Many state-of-the-art nuclear models Provide a complete description of all reactions channels and observables Influence on the calculated production cross section valuesJ. et al., https://tendl.web.psi.ch/tendl_2015/tendl2015.html Koning A.J. and Rochman D., Nucl. Data Sheets, 113, 2012TENDL2015Nuclear data library based on both default and adjusted TALYS calculations and data from other sources TENDL2015 contains evaluations for :

  O and 19 F from ENDF/B-VII.1) Novel therapeutic nuclide C. Duchemin et al., Phys. Med. Biol. 60 (2015) 931and accelerators being used in an increasing number of countries along with reactors -Diagnosis (γ, β + ) -Therapy (β -, α, e Auger ) Many useful / potentially useful isotopes identified for applications in nuclear medicine -Personalized medicine The Right Drug To The Right Patient For The Right Disease At The Right Time With The Right Dosage Nuclear data -Accurate and reliable sets of data Statistical + systematic errors < 10% -Well defined production routes and decay properties neutron, light charged particules and ions -Optimum production of specific radionuclides, minimization / elimination of impurities, realistic dose calculations, monitor reactions Nuclear codes Provide a large set of nuclear data in terms of targets, projectiles and energy range to constrain and develop predictive simulation tools of nuclear reactions

Capsule and foils Irradiation station and beam line IAEA recommended cross sections:

	-8 reactions available for protons
	27 Al (2), nat Ni, nat Ti and nat Cu (4)
	-5 reactions available for deuterons
	27 Al (2),

Act . A . ρ′ . e′ . (1 -e -λ ′ .t ) 𝜒𝜒. Act′ . A′ . ρ . e . (1 -e -λ.t )

Use of a monitor foil:

 error on e, e': ≤ 1%  error on t: negligible nat Fe, nat Ni and nat Ti -6 reactions available for alpha-particles 27 Al (2), nat Ti and nat Cu (3)


Arnaud Guertin

Charlotte Duchemin

Ferid Haddad

Etienne Nigron

Vincent Métivier

Guertin Arnaud

How nuclear data collected for medical radionuclides production could constrain nuclear codes

-Target/monitor/degrader pattern -Thin foils:

E loss small and constant -One cross section value per foil Activity and cross section:

σ = Act . A χ. Φ . 𝒩𝒩 A . ρ . e . (1 -e -λ.t ) σ = σ ′ . 𝜒𝜒 ′ .

Conclusion and outlooks

A large set of data have been collected using the stacked-foil technique at ARRONAX -with different type of projectiles (proton, deuteron and alpha particles) -for materials all over the mass range -for diagnosis and therapy purposes in nuclear medicine

Comparisons have been performed systematically with the TALYS 1.6 code -state of the art models included -possibility to combine models to better describe data -strong reactivity of authors Three main mechanisms have been studied at the moment:

-optical potential -level density description -preequilibrium model A set of models have been found to allow a good description of all our collected data, which is different from the suggested default models.

Further investigations will be done on other mechanisms that can affect our observable.

-

  available for deuterons 27 Al (2), nat Fe, nat Ni and nat Ti -6 reactions available for alpha-particles 27 Al (2), nat Ti and nat Cu (3)Use of a Faraday cup:-Beam dump placed at the end of the stack to control the intensity during the irradiation HPGe coaxial detector γ spectra recorded on 8192 channels -Dead time: < 10% (sum peak) -FWHM:1.04 keV at 122 keV ( 57 Co) -Activity values: FitzPeaks 1.97 keV at 1332 keV ( 60 Co) -T 1/2 , E γ , I γ : Lund/LBNL, NNDC -Energy and efficiency calibrations: Co and Eu γ rays used to extract production cross section of 230,232,233 Pa Target and monitor:  counted twice  during > 24 hrs  2 Th-232(p,3n)Pa-230 → U-230 U-230(21 d)/Th-226(31 min) α RIT for leukaemia treatment 4 α cascade of 27.7 MeV C. Duchemin et al., Phys. Med. Biol. 60 (2015) 931models that best describes the whole set of available data for all projectiles, targets and incident energies defined by the TALYS authors TALYS 1.6 Default One combination of models that best describes our whole set of data for proton, deuteron, alpha particles as projectile (and literature data) has been defined by C. Duchemin et al. TALYS 1.6 Adj.

Use of a monitor foil:

  Act . A . ρ′ . e′ . (1 -e -λ ′ .t ) 𝜒𝜒. Act′ . A′ . ρ . e . (1 -e -λ.t )

	 error on e, e': ≤ 1%
	 error on t: negligible

14/09 2016, Bruges, Belgium ND2016

TALYS

Code for the simulation of nuclear reactions Many state-of-the-art nuclear models

Provide a complete description of all reactions channels and observables

Nuclear reactions

Projectiles : n, p, d, t, He-3, α particles seven types of incidents particles (n,p,d,t,gamma ray) all isotopes living more than 1 second (~ 2800 isotopes) all files are original except 15 (natural carbon from JENDL-4.0, 1,2,3 H, 2,3 He, 6,7 Li, 10,11 B, 9 Be, 14,15 N, 16 O and 19 F from ENDF/B-VII.1)