Toshiya Suzuki

Improved performance in Ru∕Ta2O5∕Ru capacitors using forming gas annealing

The effects of forming gas (H2∕N2=3%∕97%) annealing (FGA) on Ru∕Ta2O5∕Ru capacitors are studied. It is confirmed that the effects of FGA highly depend on its timing in the preparation sequence. Though FGA after the patterning of the Ru top electrode results in the increased leakage current of the capacitor, FGA prior to the patterning of the Ru top electrode substantially reduces the leakage current and prevents subsequent thermal process-induced peeling between Ta2O5 and Ru, yielding the capacitor with the best electrical characteristics. Such improvements most likely originate from the formation of a stable bonded interface intrinsically linked to Ta2O5 and Ru, and the phase change from TaOx to Ta2O5.

Control of Two Types of Dielectric Relaxation Current for Ta2O5 Metal-Insulator-Metal Capacitors

Ta2O5 is the most promising high-k dielectric candidate for metal-insulator-metal (MIM) capacitors, but its dielectric relaxation (DR) currents may cause irrecoverable charge loss, although DR is a universal phenomenon of normal dielectrics. Therefore, the Ta2O5 MIM capacitors DR chasracteristics and their control were investigated. Ta2O5 DR is composed of two components. One component shows t-1-type time decay, which is assumed to be caused by nonuniformity of electron polarization and is almost of the same order as that of SiN. Thus, its influence on dynamic random access memory (DRAM) operation will be limited. The other component shows t-0.5-type time decay, which is caused by hydrogen deoxidation of Ta2O5, and is dominant in the case of deoxidized Ta2O5 DR. It causes about 16% charge loss. Namely, it will have an adverse influence on DRAM operation. N2 annealing is a possible solution for the reduction of this t-0.5-type DR.

Low Crystallization Temperature for Ta2O5 Thin Films

We confirmed that Ta2O5 thin films can be crystallized by coating it with a Ru film and then annealing in H2-containing ambient at temperatures as low as 400°C. Stoichiometric Ta2O5 is thermally stable but the TaOx phase in the Ta2O5 films disappears during H2 annealing at 400°C.

Selective and blanket tungsten interconnection and its suitability for 0.2-micron ULSI

Voids and nondeposition were observed in via holes using blanket W and sputter Al because step coverage was significantly affected by the uniformity of the glue layer and by shadowing. In studying integrated multiple metallization (IMM), it was found that selective W adequately fills via holes down to 0.2 mu m in diameter and greatly improves step coverage, with optimum coverage even after 40% via-hole filling. Blanket W and Al wiring can thus be used for high-aspect via holes, even if step coverage is poor. The contact resistance of selective W to poly-Si is lower than that of Al/TiN in 0.2- mu m contacts. Thus, metallization based on selective W satisfies interconnection requirements in gigabit-scale integration.<<ETX>>