| Summary: | 博士 === 國立清華大學 === 材料科學工程學系 === 90 === The minimization of critical dimensions in microelectronic devices gives rise to an increased density of structures per wafer. As a result, the circuit current densities and Joule heating increase with the decrease in size. In addition, at a high-density current (above 104 amp/cm2), the transport of current can displace the ions and influence the transport of mass. The mass transport by the electric field and charge carriers is called electromigration. However, the combined effects of Joule heating and electromigration were particularly serious. In this dissertation, the diffusion of metals in doped-Si, dopant activation in SOI strips, and electromigration of Ni in Ni silicides were discussed.
Scientifically, the enhanced interfacial reactions between metal contact and Si under high-density current are of interest. The interactions of electrical and chemical forces on the contact and heavily doped Si channel are also of much interest. Most of the failure mechanisms, such as polarity effect, contact reaction, silicide line formation in heavily doped Si channel and the elimination of EOR defects, on Ni (or Cu) contact pair structures of the p+-Si channel have been discussed.
Since the SOI has excellent isolation and poor heat dissipation, enhanced dopant activation and elimination of end-of-range (EOR) defects in BF2+-implanted silicon-on-insulator (SOI) have been achieved by high-density current stressing. With the high-density current stressing, the implantation amorphous silicon underwent recrystallization, enhanced dopant activation and elimination of the end-of-range (EOR) defects. The current stressing method allows the complete removal of EOR defects that has not been possible with conventional thermal annealing in the processing of high-performance SOI devices. For example, the SOI strips were implanted by 40k eV at a dosage of 5×1015 ions/cm2. The total resistance for the as-implanted SOI strips was decreased from 4.8k to 1kΩ, about 80﹪reduction, after the density of current exceeded 1.6×106 A/cm2. On the other hand, samples annealed at 900 ℃ for 30 min, the resistance of the Si strip decreased further from 480 to 450 Ω after stressing with a current of 2×106 A/cm2.
A previous investigation of Joule heating effect on thin SOI films showed that the amorphous Si induced by ion implantation had been crystallized with high density current. In addition, electric-field-enhanced recrystallization of amorphous Si has been confirmed that could reduce the crystallization temperature of amorphous Si. A method of forming low-temperature poly-Si, which uses current induced amorphous silicon recrystallization to solve problems caused by high-temperature and long-term annealing treatment has been developed. As the applied current ramping up to 4.3×107 mA/cm2 on the nickel silicide film, the a-Si layer was induced to crystallize into poly-Si suddenly. A strong polarity effect on nickel silicides enhanced poly-Si transformation was found under high-density current stressing. The enhanced diffusion of ionized Ni through NiSi2 precipitates in an electric field leads to an acceleration of the crystallization of a-Si. The crystallization, therefore, processes could be completed by electric current stressing at room temperature.
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