Electrical Reliability Issues of Integrating Low-K Dielectrics with Cu Metallization zyxw Z. C. Wu, Z. W. Shiung, C. C. Wang, K. L. Fang, R. zyxw G. Wu, Y. L. Liu, B. Y. Tsui and M. C. Chen Department of Electronics Engineering, National Chiao-Tung University 1001 Ta Hsueh Road, Hsinchu 300, Taiwan W. Chang, P. F. Chou, S. M. Jang, C. H. Yu and M. zyxw S. Liang Taiwan Semiconductor Manufacturing Company No.9, Creation Rd. I , Science-Based Industrial Park Hsinchu, Taiwan Abstract Electrical reliability issues of two organic aromatic low-K materials (K = 2.6 - 2.8) were investigated. Both materials show acceptable thermal stability and good dielectric barrier property against Cu penetration. C-V curve instability was observed under bias-tempem stress zyxwvuts (BTS) for the zyxwvut first time. It zyxwvutsrqpo can be explained by the model of stress induced dielectric polarization charges. This instability may be an issue of long term stability of circuits. Introduction Interconnect wire parasitics (wire resistance R and inwinter-level capacitance C) at 0.18 ,u m begins to overwhelm not only the overall device delay but also the packing density, reliability, and manufacturing cost of ICs (1). To alleviate the dilemma of achieving high performance ULSI circuits without sacrificing capabilities of driving speed, crosstalk tolerance and dynamic power dissipation, it appears a must to reduce the RC time delay through the use ,of new materials. Therefore, process integration of Cu and low-K dielectrics has been eagerly pursued in view of their inherent benefits such as low electrical resistivity, superior electromigmtion resistance and low dielectric constant. However, very few studies have been performed to electrically emphasize the reliability issues of integrating low-K dielectrics with Cu (2, 3). In this work, we evaluate the dielectric barrier effectiveness for Cu penetration with regard to two species of mainstream organic aromatic low- K polymers and try to qualitatively explain the novel finding on the stress induced dielectric polarization effects, which account for electrical instabilities in C-V characteristics. Experimental Electrical measurements were made on (Cu, AI)/USG(5Onm)/low-K(5OOnm)dielectric/oxide(5Onm)/p-Si oxide-sandwiched MIS capacitors. The Cu surface was M er covered with a 50nm thick TaN overlayer for the prevention of Cu oxidation. Two species of low-K dielectric were investigated; they are otganic aromatic polymers with K values between 2.6 and 2.8, and are referred to hereinafter as LKI and LK2. There is a major step of difference regarding the preparation of the LK1 and LK2 polymer samples. zyxw An adhesion promoter layer (-1 Om), whose schematic structure is illustrated in Fig. 1, was first spin-on coated on the oxide surface prior to the coating of the LK! polymer. On the other hand, this layer was not coated for the LKI sample because the adhesion promoter material WiiS synthesized into the bulk ofthe LKI polymer. After the MIS c;tpacitors were annealed at 400°C for 30 min in N, ambient, they were bias-temperature stressed (BTS) at 150°C with gate biases of 24 and 48V applied to produce electric fields of 0.4 and 0.8 MV/cm, respectively, for at least 30 min, which is long enough for the mobile charges to drift across the stacked insulator layer. High frequency C-V characteristics of the MIS capacitors were measured at a frequency of 1 MHz. In addition, the gate current of the MIS capacitors during the BTS was monitored, and the I-V characteristics were instantaneously measured zit 150°C after the BTS. Moreover, secondary ion mass spectroscopy (SIMS) was employed to probe possible presence of’Cu in the insulator layers of the MIS capacitor. X- ray photoelectron spectroscopy (XPS) as well as total reflection X-ray fluoiescence (TXRF) was used to measure the metallic trace element density residing in the polymer structure. Results and Discussion Fig. 2 shows the percentage of thickness shrinkage of HSQ (Hydrogen Silsesquioxane), LKl and LK2 films thermally annealed iri N, ambient at 400 and 450°C as a betion of annealing time. The measured data indicate that the low-K polymers show a better thermal stability than the HSQ film. In particular, the LK2 exhibits the sturdiest thermal stability. Fig. 3 shows C-V curves of the LKl and LK2 oxide- sandwiched MIS capacitors of Cu as well as A1 gate before and after BTS. For both of the low-K capacitors, it is obvious that the C-V behaviors are independent of the gate metal used. 82 0-7803-6327-2/00/$10.00 0 2000 IEEE