Browsing by Author "Jiang, JS"

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Electromigration in sputtered copper films on polyimide
(1999-06-01)
Wang, HW
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Chiou, BS
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Jiang, JS
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電子物理學系
;
電子工程學系及電子研究所
Electromigration damage (EMD) is one of the major causes for the failures of interconnects. In this study, the electromigration of Cu on polyimide is investigated. An empirical formula is used to evaluate the EMD of Cu film. The activation energy (Q) obtained is significantly less than those of lattice and grain boundary diffusion. This suggests that the electromigration in copper proceeds via an interfacial diffusion path. The geometry of the metallization also affects the activation energy. Any abrupt change in the interconnect direction and metal width causes current crowding and should be avoided. The current exponents (n), calculated from EMD data, are 3.58 and 3.35 for straight and zig-zag Cu films, respectively.
Electromigration in sputtered copper interconnection with polyimide as interlevel dielectric or passivation
(2000)
Chiou, BS
;
Jiang, JS
;
Wang, HW
;
Hung, HY
;
電子工程學系及電子研究所
Electromigration damage (EMD) is one of the major causes for the failures of interconnection. The use of copper and low dielectric constant dielectric has been proposed to reduce the RC time delay and to improve EMD. In this study, the Electromigration of Cu with polyimide is investigated with an empirical formula dR/dt.1/R-0 = AJ(n) exp(-Q/RT). Secondary ion mass spectrometry (SIMS) reveals the interdiffusion between Cu and polyimide during curing of the polyimide and/or annealing of Cu metallization. Thin layers of TiW is deposited between polyimide and Cu as a barrier to reduce the interdiffusion. The activation energy Q for the electromigration of Cu on polyimide is 0.77eV from 120 degrees C to 230 degrees C, while activation energies for samples with titanium tungsten as an interlayer are 0.79eV (140 degrees C to 190 degrees C) and 1.73eV (190 degrees C to 230"C). The presence of TiW barrier enhances the high temperature electromigration resistance and promotes the adhesion between Cu and polyimide interface. However, films with TiW are found to be more sensitive to current stressing than those without. Polyimide is also employed as a passivated layer on top of Cu metallization. Resistance of the passivated samples decrease in the initial stage of the electromigration experiment. Possible causes are discussed on the decrease in R. The geometry of the metallization also affects the electromigration, the current exponent (n), calculated from EMD data, are different for interconnection with different geometries.
ML solutions for resolving frequency ambiguity in OFDM systems
(2005)
Yu, JH
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Jiang, JS
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Su, YT
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電信工程研究所
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Institute of Communications Engineering
The conventional approach for compensating the carrier frequency offset (CFO) of OFDM signals is to estimate the fractional part of the CFO first and then resolve the remaining ambiguity, if exists, by locating the integer part. This paper gives a systematic derivation of the maximum likelihood (ML) integer CFO estimate, that takes into account the effects of channel fading and residual fractional CFO, unifying various earlier proposals. As the complexity of the resulting ML estimate is relatively high, we also suggest various near-optimal and suboptimal combinations and examine their performance. It is shown that, with judicious choice of the component terms of the ML estimate, one can obtain low-complexity integer CFO estimates with excellent performance even in the presence of highly frequency-selective fading.
The effect of polyimide passivation on the electromigration of Cu multilayer interconnections
(2001)
Jiang, JS
;
Chiou, BS
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Electromigration damage (EMD) is one of the major causes for the failures of interconnect. In this study, the electromigration (EM) of Cu multilayer (TiWN/Cu/TiWN) with polyimide passivation is investigated with an isothermal resistance change method. The EM measurements were carried out on a wafer level at various temperatures (170-230 degreesC) and current densities (2.28-4.0 MA/cm(2)). The activation energy for passivated Cu multilayer is larger than that of the unpassivated ones. The lifetime of passivated specimens are from two to 16 times those of the unpassivated ones. Resistance oscillation, which is attributed to the formation and closing of Cu gap, is observed during EM test. The TiWN interlayer helps to maintain the electrical continuity when a local Cu gap is formed. Hence, the lifetime of Cu metallization is further enhanced by the presence of the interlayer. Copper multilayer interconnect has better EMD resistance than Cu monolayer interconnect does. (C) 2001 Kluwer Academic Publishers.