Mesure in-situ de la zone fondue d'un circuit integre lors de la fabrication d'une resistance diffusee par laser.

摘要

While conventional CMOS manufacturing processes have been extensively developed and improved for digital microelectronics, they are not completely adapted for analog circuits, because of their inherent inaccuracies of the resulting resistive components. One of the methods developed to overcome these problems and improve sensitive circuits functionality is the laser diffused resistor technique (Meunier et al. 2002), consisting of irradiating the gap of a gateless field effect transistor, thus inducing the diffusion of dopants into the melted silicon and creating a resistive link. While this method has proven to be make precise resistors and accurate analog circuits, the resulting circuit functionality is still slightly sensitive to processing variations and control methods must be developed to accelerate industrial integration of this trimming technique. One such technique described in this master thesis is based on the reflectivity changes of the irradiated region that can be detected with a low power continuous wave laser. The objectives of this research are to analyse the reflected power measurements in terms of structural deformations caused by the irradiation and develop a control method for the laser diffusion resistor trimming technique.;As revealed by microstructural characterization, dielectric layers of TSMC 180 nm circuits show strong variations caused by the laser irradiation and are nearly destructed. In addition, the silicon surface takes a sombrero shape when melted. Those modifications on silicon and dielectrics can cause great variations on the reflected power that are not included in the simulation model.;Different hypothesis are proposed to explain special phenomena observed on reflected power measurement of irradiated circuits. Simulations of the silicon deformation permit to partially explain the increase of reflected power after the laser pulse. Other behaviours could be explained by the melting of the dielectrics and the interdiffusion between these layers.;It is shown that manufacturing processes can cause up to 20% of variation on the reflected power from a circuit to another one, which could greatly affect the laser diffused resistor characteristics. To overcome these variations, it is proposed to use the reflected power measurements or a specific transition time to control the laser diffused resistor fabrication process. Tests using the transition time criteria showed good results to adjust the irradiation power and permitted to reduce by 85% the diffused resistor fabrication errors on TSMC 250 nm technology. The developed method is totally compatible and can be integrated in any industrial processes.;Reflected power measurements, taken on different CMOS process technologies, are compared to those taken on bare silicon and simulation. Results on integrated circuits show a greater sensitivity to laser power and special behaviours such as a sudden decrease of the reflected power during the irradiation follow by an increase at the end of the pulse.