886 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 51, NO. 6, JUNE 2004 RF, DC, and Reliability Characteristics of ALD HfO –Al O Laminate MIM Capacitors for Si RF IC Applications Shi-Jin Ding, Hang Hu, Chunxiang Zhu, Member, IEEE, Sun Jung Kim, Xiongfei Yu, Ming-Fu Li, Senior Member, IEEE, Byung Jin Cho, Senior Member, IEEE, Daniel S. H. Chan, Senior Member, IEEE, M. B. Yu, Subhash C. Rustagi, Senior Member, IEEE, Albert Chin, and Dim-Lee Kwong, Senior Member, IEEE Abstract—High-performance metal–insulator–metal capac- itors using atomic layer-deposited HfO –Al O laminate are fabricated and characterized for RF and mixed-signal appli- cations. The laminate capacitor can offer high capacitance density (12.8 fF/ m ) up to 20 GHz, low leakage current of A/cm at 2 V and 125 C, and small linear voltage coefficient of capacitance of 211 ppm/V at 1 MHz, which can easily satisfy RF capacitor requirements for year 2007 according to the International Technology Roadmap for Semiconductors. In addi- tion, effects of constant voltage stress and temperature on leakage current and voltage linearity are comprehensively investigated, and dependences of quadratic voltage coefficient of capacitance on frequency and thickness are also demonstrated. Mean- while, the underlying mechanisms are also discussed. Index Terms—Atomic layer-deposit (ALD), HfO –Al O lam- inate, metal–insulator–metal (MIM) capacitor, radio frequency (RF), reliability. I. INTRODUCTION T HE DRAMATIC increase in wired and wireless com- munications has triggered the demand for metal–insu- lator–metal (MIM) capacitors, which can offer low parasitic capacitance, low voltage coefficients, and high quality factor for RF applications [1]. With an increase in levels of inte- gration and the scale-down of chip size, future technology generations will require integrated RF MIM capacitors with higher capacitance density in view of lower system cost. High capacitance density can be achieved by utilizing either high dielectric constant (high- ) materials or very thin insulator layers. However, leakage current and reliability issues limit the aggressive thickness scaling [2]. Therefore, high- materials are much preferred as a possible solution. In the last two years, Manuscript received September 18, 2003; revised March 2, 2004. This work was supported in part by Institute of Microelectronics (Singapore) under Grant R-263-000-235-592 and in part by the National University of Singapore under Grant R-263-000-221-112. The review of this paper was arranged by Editor G. Groeseneken. S.-J. Ding, H. Hu, C. Zhu, S. J. Kim, X. Yu, M.-F. Li, B. J. Cho, and D. S. H. Chan are with the Silicon Nano Device Laboratory, Department of Electrical and Computer Engineering, National University of Singapore, Singapore 119260 (e-mail: elezhucx@nus.edu.sg). M. B. Yu and S. C. Rustagi are with the Institute of Microelectronics, Singa- pore 117685. A. Chin is with the Department of Electronics Engineering, National Chiao Tung University, Hsinchu 30050, Taiwan, R.O.C. D.-L. Kwong is with the Department of Electrical and Computer Engineering, University of Texas, Austin, TX 78712 USA. Digital Object Identifier 10.1109/TED.2004.827367 various high- dielectrics, such as HfO [3]–[5], AlTaO [6], Tb-doped HfO [3], (HfO ) (Al O ) [7], Al O [8], [9], AlTiO [9], and Ta O [8], [10], have been explored to replace conventional silicon dioxide and silicon nitride for MIM capacitors. However, the challenge still remains to achieve high capacitance density especially in RF regime, while maintaining minimal leakage current, acceptable voltage coefficients of capacitance (VCCs), and so on under the thermal budget of a back-end process. An HfO –Al O laminate has been evaluated in metal-insu- lator-poly-silicon structure for dynamic random access memory (DRAM) application, showing excellent leakage characteristics [11], where capacitance density and leakage current are of great importance. However, in the case of RF MIM capacitors, RF performances and voltage linearity are emphasized in partic- ular. Thus, it is desirable to investigate the characteristics of the HfO –Al O laminate for MIM capacitors application. In this paper, we employed alternate 1-nm Al O and 5-nm HfO as an insulator for MIM capacitor. The 1-nm Al O layers were acted as the contacting layers to the bottom and top electrodes to improve the metal/dielectric interface quality, as suggested by Ishikawa et al. [10]. As a result, high performance MIM ca- pacitors using the atomic layer-deposited (ALD) HfO –Al O laminate have been demonstrated successfully, suggesting that it is a very promising candidate for next generation RF and mixed signal IC applications. II. EXPERIMENTS The MIM capacitors were fabricated on 4- m SiO deposited on Si wafer. The sputtered Ta–TaN layers were used as the bottom electrode, where Ta was used to reduce the parasitic resistance of the electrode and TaN served as a barrier layer. After that, the laminate dielectrics with alternate Al O (1 nm) and HfO (5 nm) layers were deposited using ALD technique at 320 C, and the beginning and end layers were 1-nm Al O , respectively. Al O were deposited using tri-methyl aluminum and water, and HfO were deposited using HfCl and water. Three thicknesses of laminate (13, 31, and 43 nm) were deposited. Then, TaN was reactively sputtered as the top electrode, followed by the forming gas annealing at 420 C for 30 min to reduce leakage current. Finally, a photolithography step and dry etching were adopted to define the MIM capacitors. In consideration of RF characterization, the coplanar transmission lines were 0018-9383/04$20.00 © 2004 IEEE