Optimization of Pulsed Annealing Techniques for GaAs Integrated Circuits
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Hess,
and Sigmon,
eds.
Laser and Electron-Bea. Solid i-.teractions and Materials Processing
299
OPTIMIZATION OF PULSED ANNEALING TECHNIQUES FOR GaAs INTEGRATED CIRCUITS
G.M. MARTIN+, A MITONNEAU+, M. CATHELIN+, S. MAKRAM-EBEID+, C. VENGER+, D. BARBIER++ AND A. LAUGIER++ +Laboratoires d'Electronique et de Physique Appliquee, 3, Avenue Descartes, 94450 Limeil-Brevannes (France), ++L.P.M., INSA, 20 Avenue Albert Einstein, 69621 Villeurbanne (France)
ABSTRACT Ohmic contacts on GaAs were realized by pulse annealing AuGe and AuGe-Ni layers deposited on top of n-type GaAs conducting layers. We used focused and large diameter YAG laser beam pulses (X = 1.06 pm), a large diameter Ruby laser beam pulse (X = 0.69 pm) and a large diameter electron beam pulse. We tested the electrical quality of the contacts obtained. We also examined the compatibility of the alloying techniques used with the self-alignment technology for IC fabrication. In particular, we tested the quality of Al Schottky diodes and of the boron implanted insulating regions which coexist on the same IC with the ohmic contacts and are subject to the same pulse annealing treatment. The relative merit of the different pulse treatments are discussed.
INTRODUCTION Pulsed annealing techniques have been proposed as a method for quality improvement of GaAs ohmic contacts. In the present state of the art, based on furnace annealing, there still remain the problems of improving the repeatability and surface morphology of these contacts to make them reliable and stable under high current operation. Most of the studies have been devoted to the electrical activation of high donor ion doses implanted in GaAs. The aim of such studies has been to reach very high donor concentrations close to the surface of the material in order to get ohmic contact by direct evaporation of a metal electrode without subsequent thermal annealing. Some encouraging values of the specific contact resistance (generally above 10-6qcm2) have been obtained in that way (1-3), but many problems of homogeneity and morphology of the GaAs surface are encountered because the energy density needed is very close to the threshold of surface damage (4) and the energy density window to be used is found to be very narrow. Furthermore, in certain conditions of laser annealing and in capless samples, a thin resistive surface layer is encountered (4-6) and prevents ohmic contact fabrication by a simple metallization (1). Another technique for the realization of ohmic contacts has been investigated more recently (7). It consists in pulsed alloying AuGe evaporated layers. This technique presents some advantages which have been studied in details and will be presented in this paper. We must note that contact quality is not the only important feature to be studied for integrated circuits applications. In particular, one must test the compatibility of the pulsed annealing treatment proposed with other steps involved in the manufacture of GaAs ICs and in particular with the self-alignment technology. In this techno
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