Laser tuning silicon microdevices for analogue microelectronics (original) (raw)
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New technologies for microelectronics devices processing by laser locally structural modifications
2008 International Semiconductor Conference, 2008
The process model involving the calculation of the laser melted region in which the dopant diffusion occurs has been developed. Experimental results are well described by the proposed modelIn this paper after reviewing the principle of our technique, we present the electronic characterization and the modeling these new microdevices and show that they present excellent current voltage linear behavior at usual microelectronics voltages. Furthermore, process modeling bases on the laser induced silicon melted region calculation is introduced and successfully compared to experimental results. The laser trimming applications for microelectronisc special components will confirm wide applications range of this new technology
A novel laser trimming technique for microelectronics
Applied Surface Science, 2002
A novel laser trimming technique, fully compatible with conventional CMOS processes, is described for analogue and mixed microelectronics applications. In this method, a laser beam is used to create a resistive device by melting a silicon area, thereby forming an electrical link between two adjacent p-n junction diodes. These laser diffusible resistances can be made in less than a second with an automated system and their values can be in the range of 100Ω to a few MΩ, with an accuracy of 50ppm, by using an iterative process. In addition, these resistances can also be made to possess a thermal coefficient close to zero. We present the method used to create these resistances, the main device characterization and some insight on the process modeling.
Laser doping for microelectronics and microtechnology
Applied Surface Science, 2005
The future CMOS generations for microelectronics will require advanced doping techniques capable to realize ultra-shallow, highly doped junctions with abrupt profiles. Recent experiments have shown the potential capabilities of laser processing of ultra shallow junctions (USJ). According to the International Technology Roadmap for Semiconductors, two laser processes are able to reach the ultimate predictions: laser thermal processing or annealing (LTP or LTA) and gas immersion laser doping (GILD). Both processes are based on the rapid melting/solidification of the substrate. During solidification, the liquid silicon, which contains the dopants, is formed epitaxially from the underlying crystalline silicon. In the case of laser thermal annealing, dopants are implanted before laser processing. GILD skips the ion-implantation step: in this case the dopants are chemisorbed on the Si surface before the laser-shot. The dopants are then incorporated and activated during the laser process. Activation is limited to the liquid layer and this chemisorption/laser-shot cycle can be repeated until the desired concentration is reached. In this paper, we investigate the possibilities and limitations of the GILD technique for two different substrates: silicon bulk and SOI. We also show some laser doping applications for the fabrication of micro and nanoresonators, widely used in the MEMS Industry. #
Finite Element Simulation Of Laser-Induced Diffusion In Silicon
Energy Procedia, 2011
Laser-assisted diffusion of dopants is a promising way to realize selective emitter solar cells with a reduced number of technological steps. This paper discusses the simulation by finite element method of laser doping in order to optimise the fabrication process. A finite element method is used to solve the heat-transfer equation which describes the thermal effects and Fick's second law which describes the diffusion of dopants. The phosphosilicate glass (PSG) layer that is produced during the emitter formation on p-type silicon solar cells is used as the doping source during the laser-assisted diffusion process. The influence of laser parameters and material properties are studied. Modelling results are compared to SIMS measurements of the phosphorous doping profile. A structure is discussed in the perspective of a self-aligned process for selective emitter fabrication, where the PSG layer is present underneath the silicon nitride (SiN x) passivation layer.
Applied Physics …, 2010
We demonstrate single dopant implantation into the channel of a silicon nanoscale metal-oxide-semiconductor field-effect-transistor. This is achieved by monitoring the drain current modulation during ion irradiation. Deterministic doping is crucial for overcoming dopant number variability in present nanoscale devices and for exploiting single atom degrees of freedom. The two main ion stopping processes that induce drain current modulation are examined. We employ 500 keV He ions, in which electronic stopping is dominant, leading to discrete increases in drain current and 14 keV P dopants for which nuclear stopping is dominant leading to discrete decreases in drain current. a 2 Classical metal-oxide-semiconductor field-effect-transistors (MOSFETs) fabricated by industrial methods are now sufficiently small that random variations in the number and placement of dopants results in inconsistent behaviour. This is already a major issue in the microelectronics industry for devices operating at room temperature. 1 Further, the Bohr radius of a donor electron is now a significant fraction of the device size resulting in the possibility of quantum mechanical dependent functionalities as observed with adventitiously doped devices at 4 K. 2-4 Emerging deterministic doping technologies aim to mitigate statistical fluctuations in the doping of these devices while also providing significant potential for solid-state quantum computers. Low energy single dopant implantation into micronscale devices has been reported. 9,10
Thin Solid Films, 2010
Due to the continuous CMOS transistor scaling requirements, highly doped shallow junctions with improved activation have been widely investigated in recent CMOS technologies. In this scope, sub-melt millisecond laser annealing has been introduced in the integration flows to enhance dopant activation, without any additional detrimental diffusion. This MSA step impacts not only the transistor junction properties, but also the polysilicon gate depletion. This paper is devoted to the study of the MSA influence on boron and germanium co-implanted polysilicon films. A sensitive boron diffusion occurring during the laser anneal step, with or without an initial spike annealing step, has been observed. The activation energy of the boron diffusivity extracted from SIMS profiles in the laser only sequence has been found equal to 4.05 eV. In addition, it was shown that either a high temperature laser anneal sequence or a spike anneal followed by a laser anneal sequence can reach the same activation levels.
Optically Controlled Silicon MESFET Modeling Considering Diffusion Process
2007
An analytical model is proposed for an optically controlled Metal Semiconductor Field Effect Transistor (MESFET), known as Optical Field Effect Transistor (OPFET) considering the diffusion fabrication process. The electrical parameters such as threshold voltage, drain-source current, gate capacitances and switching response have been determined for the dark and various illuminated conditions. The Photovoltaic effect due to photogenerated carriers under illumination is shown to modulate the channel cross-section, which in turn significantly changes the threshold voltage, drainsource current, the gate capacitances and the device switching speed. The threshold voltage V T is reduced under optical illumination condition, which leads the device to change the device property from enhancement mode to depletion mode depending on photon impurity flux density. The resulting I-V characteristics show that the drain-source current IDS for different gate-source voltage V gs is significantly increased with optical illumination for photon flux densities of Φ = 10 15 and 10 17 /cm 2 s compared to the dark condition. Further more, the drain-source current as a function of drain-source voltage V DS is evaluated to find the I-V characteristics for various pinch-off voltages V P for optimization of impurity flux density Q Diff by diffusion process. The resulting I-V characteristics also show that the diffusion process introduces less process-induced damage compared to ion implantation, which suffers from current reduction due to a large number of defects introduced by the
Characteristics of Short-Channel Mosfet's in Laser Crystallized Si-on-Insulator
MRS Proceedings, 1983
ABSTRACTData are reported on short-channel MOSFET's fabricated in laser crystallized silicon-on-insulator (SOI) structures. In this experiment, special effort was made to minimize enhanced diffusion of dopants from the source and drain regions along grain boundaries. Instead of the standard anneal used for the implant activation, rapid thermal annealing and low temperature furnace annealing were used. These modified processes yielded functional MOSFET's with channel lengths as short as 1.5 μm, and ring oscillators of 2.0 μm. A speed of 115 ps per stage was obtained in these ring oscillators which is not only the fastest ever reported on any SOI structure, but also a factor of 2 faster than that from the same circuits in bulk Si. The results demonstrate quantitatively the speed improvement of SOI over bulk material due to reduced parasitic capacitance.
Focused pulsed visible laser used in laser-trimming technologies such as the laser diffused-resistor process may inject charges in the semiconductor, leading to an interaction with highly sensitive circuits. In order to evaluate the process impact on those circuits, a study of the perturbation on the free-running frequency of a ring oscillator due to a nearby laser pulse has been made. The behavior of this modification as a function of the laser-pulse power exhibits complex features. A thermodynamics and electrical model of the charge injection by a focused pulsed laser on silicon has been developed. First, the laser-induced charge diffusion is calculated by a finite-element-model coupling Boltzmann semiclassical transport and thermodynamic equations; the last one being necessary, as relatively high laser power may increase significantly the local temperature. The result is then fed into an electrical model of the ring oscillator as a perturbation injected by a current source. This model coupled to parasitic-light effects due to geometrical changes during silicon melting is able to explain the oscillator's operation-frequency modification.