Laurent Jalabert

Alternative approach in 3D MEMS-IC integration using fluidic self-assembly techniques

Nowadays, industries are investigating new, original and appropriate solutions to address challenges in 3D MEMS-IC large-scale integration. Self-assembly techniques are among those. We report on an alternative approach inspired from fluidic self-assembly and using the flip-chip method. Here, solder bumps are directly formed onto a MEMS chip using liquid solder solution in a bath. The self-alignment process is operated after surface treatment by plasma deposition to form high and low wettability selective patterns. Finally, MEMS and electronic chips are permanently bonded after low thermal heating without any pressure. Electrical contact is established and electromechanisms of the microsystems are proven. Compared to classic MEMS-IC flip-chip methods, this strategy presents many advantages: it is a low-cost and fast fabrication process requiring no specific equipment for deposition of solder bumps. Furthermore, it can be applied on different substrates and it does not require a specific pressure method during the bonding process. This strategy is also an appropriate fabrication method for large-scale MEMS integration where electronic connection density is high.

Boron Diffusion and Activation during Heat Treatment in Heavily Doped Polysilicon Thin Films for P+ Metal-Oxide-Semiconductor Transistors Gates

In this work, we present a study of heavily doped polycrystalline silicon which is used as a transistor gate in standard complementary metal-oxide-semiconductor (CMOS) technology. Our aim is to study the redistribution and activation of boron during thermal annealing in thin silicon films implanted and deposited by low-pressure chemical vapor deposition (LPCVD) using a disilane (Si2H6) gaseous source. The boron concentration is monitored by secondary ion mass spectrometry (SIMS). The resistivity measurements by the four-probe method show that the films become conductors after annealing. Carrier mobility and active doping fraction are obtained by Hall effect measurements. To investigate the SIMS profiles, we have proposed a model based on the one-dimensional numerical resolution of Ficks laws. This model takes into account phenomena due to effects of very heavy doping such as that of clusters. The boron diffusion coefficient and its activation percentage are deduced from the adjustment of simulated profiles with SIMS experimental ones. We have used SUPREM IV software in order to estimate the boron diffusion coefficients in these films and compare them to our results. A small gap between the profiles simulated by our model and by SUPREM IV has been observed, in particular in the region where the boron limit solubility is exceeded. Nevertheless, the diffusion coefficient values obtained by the two methods are of the same order of magnitude.

Boron diffusion into nitrogen doped silicon films for P+ polysilicon gate structures

Abstract This paper deals with the study of the boron diffusion in nitrogen doped silicon (NIDOS) deposited from disilane Si 2 H 6 and ammonia NH 3 for the development of P + polysilicon gate metal oxide semiconductor (MOS) devices. NIDOS films with varied nitrogen content have been boron implanted, then annealed and finally analysed by secondary ion mass spectroscopy (SIMS). In order to simulate the experimental SIMS of boron concentration profiles in the NIDOS films, a model adapted to the particular conditions of the samples elaboration, i.e. the very high boron concentration and the nitrogen content, has been established. The boron diffusion reduction in NIDOS films with increasing nitrogen rates has been evidenced by the profiles as well as by the obtained diffusion coefficients, which shows that the nitrogen incorporation reduces the boron diffusion. This has been confirmed by capacitance–voltage ( C – V ) measurements performed on MOS capacitors: the higher the nitrogen content, the lower the flat-band voltage. Finally, these results demonstrate that the improvement of the gate oxide quality occurs with the suppression of the boron penetration.

Properties of nitrogen doped silicon films deposited by low pressure chemical vapour deposition from disilane and ammonia

Abstract Nitrogen doped silicon films have been deposited by low pressure chemical vapour deposition from disilane Si 2 H 6 and ammonia NH 3 . Deposition kinetics is investigated, pointing out the influences of the deposition temperature, the total pressure and the gas flow rates. According to the Bruggeman theory, variations of the NH 3 /Si 2 H 6 gaseous ratio allow for a wide range of the SiN x stoichiometry as well as a good control of the film nitrogen doping. The different behaviours of the nitrogen atom in silicon films are discussed and an overview of the nitrogen doped silicon physical properties (optical, mechanical and electrical) is proposed for the development of boron-doped polysilicon gates.

Ballistic Thermal Conductance of a Lab-in-a-TEM Made Si Nanojunction

The thermal conductance of a single silicon nanojunction was measured based on a Lab-in-a-TEM (microelectromechanical systems in a transmission electron microscope) technique and was found to be at least 2 orders of magnitude larger than the ones of long nanowires in the 380-460 K temperature range. The predominance of ballistic phonon transport appears as the best hypothesis to retrieve quantitative predictions despite the geometrical irregularity of the junction. The measurement is based on a MEMS structure including an electrostatic actuator that allows producing nanojunctions with the accuracy based on the resolution of a transmission electron microscope. The thermal conductance is measured by two integrated resistors that are simultaneously heating and measuring the local temperatures at the nearest of the nanojunction. The considerable thermal conductance of short nanojunctions constitutes a new key element in the design of nanosystems and in the understanding of the damaging of mechanical micronanocontacts. This conducting behavior is also paving the way for the development of nanoscale cooling devices as well as of the recent phononic information technology.

Real-time transmission electron microscope observation of nanofriction at a single Ag asperity

The observation of nanoscale deformation in real time is a significant step toward understanding the mechanisms of friction and lubrication. Our experimental setup of a micromachine combined with a transmission electron microscope allowed us to measure the deformation, force and cross-sectional area of a single Ag asperity during shear testing. The experimental results provided insight into one of the parameters that determines the frictional coefficient. Furthermore, we demonstrated that the energy loss associated with a shear fracture event is strongly correlated with the increase in total surface energy of the two surfaces formed here after the fracture of the nanocontact.

Reduction of boron penetration through thin silicon oxide with a nitrogen doped silicon layer

Abstract This paper deals with the development of the disilane Si 2 H 6 gaseous source for gate technology and more precisely, reports on the use of nitrogen doped silicon (NIDOS) deposited from disilane and ammonia for the realisation of polycrystalline gate. Boron diffusivity into the NIDOS films is studied thanks to SIMS experiments, and results are extended to the fabrication of P + -poly-Si/NIDOS/SiO 2 /Si capacitive structures. Electrical characterisations evidenced finally the influence of boron and nitrogen atoms on the electrical properties of PMOS devices.

Improvement of Silicon Nanotweezers Sensitivity for Mechanical Characterization of Biomolecules Using Closed-Loop Control

In this paper, we show that closed-loop control can be advantageously used for the characterization of mechanical properties of biomolecules using silicon nanotweezers (SNT). SNT have already been used in open-loop mode for the characterization of mechanical properties of DNA molecules. Up to now, such an approach allows the detection of stiffness variations equivalent to about 15 DNA molecules. Here, it is shown that this resolution is inversely proportional to the resonance frequency of the whole system and that real-time feedback control with state observer can drastically improve the performances of the tweezers used as biosensors. Such improvement is experimentally validated in the case of the manipulation of fibronectin molecules. The results are promising for the accurate characterization of biopolymers such as DNA molecules.

Mechanical Characterization of Biomolecules in Liquid using Silicon Tweezers with Subnanonewton Resolution

Molecular biophysicists seek to understand how biological systems work through mechanical or electrical characterizations performed at the molecular scale. From this perspective, we have devised a silicon-based micromechanical tool for stress-strain measurements of molecular fibers and demonstrated micromanipulation and biomechanical characterization of DNA bundles in a liquid solution. By combining this instrument with a microscopic displacement measurement technique based on Fourier transform image processing, we could achieve a force resolution of 25 pN - a level which is within the single-molecule sensing range - and validate a novel approach for stress-strain measurements.

Boron diffusion and activation in polysilicon multilayer films for P+ MOS structure: Characterization and modeling

This work deals with in situ boron diffusion and activation in multilayer films: polysilicon (Poly1)/amorphous silicon (Poly2). These films are deposited by LPCVD technique. However, several heat treatments were carried in order to determine the optimal annealing conditions to suppress boron penetration from the gate to the substrate through the gate oxide in MOS structure. The boron concentration is monitored by secondary ion mass spectrometry (SIMS). To investigate SIMS profiles we proposed a model of boron diffusion into these multilayer structures. It is important to note that the parameter values of the studied films such as the diffusion coefficient, the activation percentage of boron as well as the acceleration rate of boron diffusion are deduced from adjustment of simulated profiles with experimental profiles. From these results, we inferred that the boron is electrically active and its distribution does not reach the oxide layer and consequently, the Poly2 may reduce the boron diffusion in optimal annealing conditions.