Effect Of RTA On TiN Films As The Barrier Layer for Pt/BST/Pt Capacitors Prepared by RF Magnetron Co-sputter Technique A
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Effect Of RTA On TiN Films As The Barrier Layer for Pt/BST/Pt Capacitors Prepared By RF Magnetron Co-sputter Technique At Low Substrate Temperature Miin-Horng Juang 1, Chuan-Chou Hwang, and Huang-Chung Cheng Department of Electronics Engineering and Institute of Electronics, National Chiao Tung University, 300 Hsinchu, Taiwan, R.O.C. 1 Department of Electronics Engineering, National Taiwan University of Science and Technology, Kee-Lung Rd., 106 Taipei, Taiwan, R.O.C. ABSTRACT Effect of rapid-thermal-annealing on metallic barrier TiN against the interdiffusions of Ti and Si into BST in Pt/BST/Pt/TiN/Ti/Si capacitors has been studied. In the integration of BST capacitors, the thermal budget of the BST deposition would cause the inter-diffusions of Ti and Si from Ti adhesion layer and Si-plug respectively. This event would degrade the BST capacitors. To address this issue, rapid-thermal-annealed TiN barriers were used between the bottom electrode Pt and adhesion layer Ti. Optimal RTA condition for TiN were found in this experiment. Excellent electrical characteristics of Pt/BST/Pt/TiN/Ti/Si capacitors, including high dielectric constant (εr =320), low leakage current (1.5x10-8 A/cm2) under 0.1 MV/cm, and life time longer than 10 year lifetime under 1.6 MV/cm were obtained with Ar+O2 mixed ambient at a low substrate temperature (300 ). INTRODUCTION One of the most crucial issues for giga era dynamic random access memory (DRAM) has long been maintaining sufficient storage charge in the small memory cell. The adoption of high dielectric constant materials simplifies the cell structure [1,2] and maintains immunity against soft error [3,4,5]. Therefore, thin barium strontium titanate (BST) film with a high dielectric constant has attracted great attention for practical use in DRAM capacitors. Among several deposition methods, 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. In general, to improve the adhesion and the contact properties via of TiSix formation, the Ti layer was deposited between the bottom electrode Pt and the Si substrate [6,7]. However, 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 O7.11.1
interaction of the bottom electrode and the Ti layer. To prevent the electrodes and dielectrics from chemical reaction with poly-Si plug and Ti adhesion layer during BST deposition and post processes, a diffusion barrier was also required. In this study, we have investigated the effect of rapid thermal annealing (RTA) on TiN barrier layer on the resultant BST capacitors. The effect of RTA treated TiN against the inter-diffusion between Si and Ti atoms has also been extensively examined via electrical and material analyses. EXPERIMENTAL DETAILS The structure of Pt/BST/Pt/TiN/Ti/Si was employed to simulate the practical capacitor over bit-line (COB) DRAM’s capac
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