TEMPERATURE DISTRIBUTION IN SI-MOSFETS STUDIED BY MICRO RAMAN-SPECTROSCOPY

The local rise of lattice temperature in n-MOS-FET's is analyzed by the energy shift of the silicon optical phonon using Raman spectroscopy with submicrometer spatial resolution. Operating the devices in saturation a source-drain temperature asymmetry is observed corresponding to the heat dissipation profile that peaks in the pinch-off region. In the substrate surrounding the transistor an anisotropic temperature distribution is found which is related to the geometric shape of the heat source. A reduction of channel length under standard conditions leads to a local temperature increase due to the higher power density. We found temperature increases of less than 20 K for an operating voltage of 5 V for a channel length down to 0.3-mu-m. The experimental results are in good agreement with a model calculation based on idealized device parameters. The time constant of transient heating under pulse operation is determined by analyzing the inhomogeneous broadening of the Raman line. Thermal time constants of about 200 ns are obtained.