In-Situ Resistance Measurements During Rapid Thermal Annealing for Process Characterization
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*IRM Research Division, Yorktown Heights, NY 10598
ABSITRACT Nieasurenient of resistance in-.situ during rapid thermal annealing is a powerful technique for process characterization and optimization. A major advantage of in-situ resistance measurements is the very rapid process learning. With silicides, in-situ resistance measurements can quickly determine an appropriate thermal process in which a low resistance silicide phase is formed without the agglomeration or inversion ofsilicide/polycrystalline silicon structures. One example is an optimized two step anneal for CoS12 formation which was developed in less than one clay. Examples of process characterization include determining the phase formation kinetics of TiSi) (C49 and C54), Co 2Si, and CoSi 2 using in-situ ramped resistance measurements. The stability of TiSi 2 or CoSi 2 /poly-Si structures has also been characterized by isothermal mneasrrrements. Resistance measurements have been made at heating rates from I to 100°C/s and temperatures up to 1000VC. The sanmple temperature was calibrated by melting Ag, Al, or Au/Si eutectics. INTROI)I)CI'TI)N Rapid thermal anmealing (RTA) is increasingly used in the microelectronics industry for a number of applications such as the processing of silicides, typically TiSi 2 or CoSt 2. Generally, during silicide processing, an optimization is needed between sufficient annealing to form the desired low resistance phase (C54 TiSi 2 or CoSi 2) and excessive annealing which causes morphological degradation such as agglomeration or inversion of silicide/polycrystalline Si structures. It is often necessary to explore and characterize an extensive parameter space and determine the kinetics of a variety of processes. An advantage of in-situ resistance measurements is that a detailed history of the reaction as a function of temperature can be acquired rapidly, resulting in a more rapid process optimizationl. In this work activation energies, E.'s, have been determined for silicide formation using ramped resistance measurements and for silicidle/poly-Si agglomeration or inversion using isothermal resistance measurements. For ramped in-situ resistance measurements, the Ea's were calculated using a Kissinger-like method where the ternperatire corresponding to a fixed stage of transformation is measured as a function of the heating rate. The activation energy can be determined from the slope of the straight line obtained by plotting ln(l/TP2(dT/dt)) versus I/Tp where T P is the temperature of the peak transformation rate anrd dT/dt is the heating rate. For convenience, we will refer to these as Kissinger plots. Details of this method can be found in the references 2 3 . For the isothermal anneals, the E. was determined from the slope of the natural logarithm of the annealing time required to reach a fixed stage of transformation versus inverse temperature for a variety of anmealing temperatures. Samples were prepared by evaporating Ti or Co on either poly-Si on oxidized or single crystal Si on sapphire (SOS) substrates. The wafers wer
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