Effect of TiN Treated by Rapid Thermal Annealing on Properties of BST Capacitors Prepared by RF Magnetron Co-sputter Sys
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ABSTRACT In this work, (Ba0o7Sr 0.3)TiO 3 thin films on Pt/TiN/Ti/Si substrate were deposited by an RF magnetron co-sputter system at 300°C in an Ar+0 2 mixed ambient. In the integration of BST capacitors, the diffusion barrier (TiN) under bottom electrodes is one of the key issues. To obtain a stable and excellent diffusion barrier against inter-diffusion between Pt and Si, as well as against being oxidized during BST deposition, TiN was treated by a rapid thermal annealing (RTA) process. Experimental results indicated that proper RTA treatments resulted in a superior TiN barrier layer. In addition, low substrate temperature during BST deposition suppressed the phenomena of inter-diffusion and barrier oxidation. Furthermore, Pt hillocking, another problem during BST deposition because of high thermal budget, was also solved by reducing substrate temperature during BST deposition. The MIM (Pt/BST/Pt) structure was used in the experiments for electrical properties measurement. High dielectric constant (cr =300), low leakage current (l.5x108 A/cm 2) under 0.1MV/cm, and 10 year lifetime under 1.6MV/cm were achieved with an Ar+0 2 mixed ambient at a low substrate temperature (300°C). INTRODUCTION
In order to maintain the required storage capacitance while shrinking the area of the DRAM cell, capacitor technology with high dielectric constant material has been very promising in the development of Giga-bit DRAM applications [1,2]. Advanced DRAMs are making use of simple capacitor structures comprised of a high dielectric constant material such as barium strontium titanate (BST) with platinum electrodes. This structure, which has the potential to store a sufficient charge for operation as a DRAM memory cell, requires very few fabrication steps and occupies a small area compared to traditional capacitor fabrication processes. Among several deposition methods, an RF magnetron co-sputter system was chosen to deposit BST thin films in this work because it is a mature and easily controlled technology for thin film deposition. The diffusion barrier under bottom electrodes is one of the key issues for the integration of BST capacitors. It is usually required to prevent the electrodes and dielectrics from reacting with Si atoms which diffuse from the poly-Si plug during BST deposition and post-deposition processing. As well, the diffusion of Ti atoms from the Ti adhesion layer into the electrodes and dielectrics is prevented by the diffusion barrier, if the Ti layer is used to form TiSix with poly-Si. TiSi, can reduce the contact resistance between TiN and poly-Si, and the adhesion between them is improved [3]. But higher leakage current density will be found if the diffusion of Ti atoms from the Ti adhesion layer cannot be suppressed, and the work function of bottom electrode materials decreases due to the interaction of the bottom electrode and the Ti layer. Besides, the Ti 37
Mat. Res. Soc. Symp. Proc. Vol. 596 © 2000 Materials Research Society
adhesion layer may diffuse up to the BST film to react with oxygen and change t
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