Wide Band Frequency Characterization of High Permittivity Dielectrics (High-K) for RF MIM Capacitors Integrated in BEOL T. Lacrevaz 1 , B. Fléchet 1 , A. Farcy 2 , J. Torres 2 , T.T. Vo 1 , C. Bermond 1 , O. Cueto 3 , E. Defaÿ 3 , M. Gros-Jean 2 , B. Blampey 1 , G. Angénieux 1 , J. Piquet 1 , F. de Crécy 3 1 LAHC, Université de Savoie, Bâtiment Le Chablais, 73376 Le Bourget du Lac, France 2 STMicroelectronics, 850 rue Jean Monnet, 38926 Crolles Cedex, France 3 LETI CEA Technologies Avancées, 17 rue des Martyrs, 38054 Grenoble, France. Phone: 33 4 79 75 87 46, fax: 33 4 79 75 87 42, email: thierry.lacrevaz@univ-savoie.fr Abstract High permittivity insulators (High-K) are progressively introduced in high-speed integrated passives and devices in order to optimize circuits performances. However, High-K properties are expected to vary with frequency as relaxation and resonance mechanisms occur. It is necessary to analyze and evaluate High-K behaviour from DC to microwave frequency. Real permittivity (K or ε’ r ) and losses (ε” r ) extraction is required over a wide band of frequency to select the most suitable insulator. The proposed method enables the characterization of as deposited thin (down to 60 nm) planar dielectrics integrated below a copper coplanar wave-guide up to 40 GHz. Results of Ta 2 O 5 and STO insulators are presented in this paper. Introduction A solution to improve integrated circuits performances, speed and integration density, consists in including High-K materials in MOS transistors [1] and MIM capacitors [2] manufacturing. Devices integrate high permittivity dielectrics to reduce gates size without increasing current leakage. Capacitors incorporate High-K to obtain high capacitances and decrease their dimensions. Several High-K value insulators, such as Si 3 N 4 , Ta 2 O 5 , HfO 2 or STO [3] seem appropriate for integration regarding their low frequency characteristics. However, dielectric K-value (K or ε’ r ) and losses (ε” r ) vary with frequency as theory predicts [4]. Relaxation and resonance phenomenon illustrated in Fig. 1 may occur. Such dielectric behaviour has to be investigated over a large spectrum to select the most appropriate candidate with low losses and enough frequency stability. Moreover, the lack of maturity of High-K materials under development usually limits their integration to the most basic processes (i.e. planar deposition). Thus, the innovative method presented in this paper was developed to analyze insulator performances on a wide range of frequencies, typically from 40 MHz to 40 GHz, before their maturity (compatibility with industrial manufacturing processes) enables their integration among conventional circuit test structures. The employed in-situ technique, based on an optimized test structure encapsulating a High-K material under test, leads to the extraction of dielectric characteristics, complex permittivity ε r (1) or/and loss tangent tgδ (2), which integrity is preserved in spite of real process environment. Results on permittivity real and imaginary parts of High-K insulators such as Ta 2 O 5 , HfO 2 and STO are discussed. Characterization method The investigated test structure is a coplanar wave-guide (CPW) integrated according to 120 nm technology design rules above the High-K dielectric to be evaluated, as shown in Fig. 2 and Fig. 3. The advantage of a coplanar wave-guide is the strong dependence of its propagation exponent Ȗ (electromagnetic property) on surrounding material characteristics, in this case: High-K insulator features. First, planar layers of SiN, SiO 2 , and High-K insulator under evaluation are deposited on 200 mm silicon wafers. The High-K under test is encapsulated by an etch-stop SiN film before deposition of a SiO 2 layer. Then, according to a standard single damascene architecture, SiO 2 layer is selectively etched down to the SiN etch-stop layer and the patterned structure is filled with copper and chemical- mechanically polished. Copper Copper Copper Coplanar Wave Guide (CPW) SiO 2 High-K : Ta 2 O 5 SiN etch stop layer Fig. 2 SEM cross section of a structure with Ta 2 O 5 Fig. 1 Real permittivity and losses of frequency dependent dielectrics K value losses Dipolar relaxation Ionic relaxation Electronic relaxation ε' r = 1 Frequency ~10 15 Hz K or ε' r ε'' r ~10 10 Hz ~10 6 Hz Frequency resonance 78 1-4244-0103-8/06/$20.00/©2006 IEEE