Ir02/(Ba,Sr)Ti03/Pt Storage Cells for 4 GBit DRAMs and Beyond: Ir, BST, and Selective Pt MOCVD and Interfacial Phenomena

Arizona State University, Scottsdale AZ

Investigators

Abstract

Sandip Dey ECS-0000121 Barium strontium titanate, (Ba, Sr)TiO3 or BST, films with high permittivity are being considered for numerous applications including charge storage cells for 4, 16, and 64 gigabit (Gb) dynamic random access memories (DRAMs). The realization of Gb DRAMs with long refresh times is contingent upon the fabrication of electrically-reliable, trench IrO2/(Ba, Sr)TiO3/Pt storage cells on Si by manufacturable, metal-organic chemical vapor deposition (MOCVD) processes. Currently, the research efforts of our laboratory are focused on MOCVD of Ir, Pt, and BST, coupled with nanostructure evolution, electrical characterization, and modeling of interfaces. A critical issue that remain unresolved, which may eventually determine the refresh time, is the lack of understanding of the effects of interfacial space charge on the transient current and dielectric dispersion of the trench capacitor. Therefore, to realize mechanically robust, trench test cells, satisfying the geometric and electrical requirements of a 4 Gbit DRAM cell, a systematic and vertically-integrated program will be implemented to: a) fabricate trench IrO2/(BST)/Pt test cells on TaxSiyNz-passivated poly-Si plugs by sequential deposition of (i) Pt by MOCVD and/or sputtering, (ii) conformal BST by MOCVD, followed by photolithography, etching, and focused ion beam (FIB) milling of BST to define the geometry of one 4 Gbit cell, and (iii) conformal Ir by MOCVD followed by its oxidation, photolithography, and etching b) quantitatively determine the space charge distribution at the Schottky BST/Pt interface in a test trench and its relationship to transient current, and dielectric dispersion by frequency and time domain techniques c) optimize BST MOCVD parameters, from feedback of electrical characterization, by response surface analyses; fabricate cells with the required electrical performance The integration of the aforementioned ideas to fabricate the next generation of storage cells will be challenging but novel, and the concepts may well be extended to the 64 Gb level. A successful outcome will provide a solution for fabricating storage cells with longer refresh times. Arizona State University (ASU) is the appropriate place to initiate such an exciting research program. The PI has carried out research on MOCVD of dielectrics and metals, and interfacial phenomena in perovskite films over the last decade. An interdisciplinary approach will train personnel in a technologically important area, so that they can apply their science and engineering skills in the US industries and research laboratories upon completion.