Method of Determining Electromigration (EM) Lifetimes and Lifetime Criteria
First Claim
1. A method for improving the design of integrated circuits (ICs) by improving resistance to electromigration failure, the method comprising:
- for a candidate IC design, varying current density j and interconnect length L through a range of values for each interconnect and, at each set of values, determining a lifetime until electromigration failure with a Technology Computer Aided Design (TCAD) computer simulation; and
,constructing one or more charts of lifetime as functions of j and L; and
,extracting from these one or more charts, one or more regions of safety from electromigration failure, one or more electromigration failure regions, and one or more aware regions of neither safety nor failure; and
,correlating the safety, failure, and aware regions with ranges of the product jL; and
,determining susceptibility to electromigration failure for interconnects within the integrated circuit by computing the product jL for each interconnect and determining if it falls in a safe, failure, or aware region, andredesigning the IC for those interconnects in the failure region so as to move the jL product out of the failure region.
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Abstract
Methods are described for performing detailed Technology Computer Aided Design (TCAD) simulations of electromigration (EM) failure in a standard test structure suitable for the simulation of integrated circuit (IC) conductive interconnects. Methods are described for performing these simulation so as to extract from the results of these simulations criteria substantially underlying the EM lifetime of interconnects, thereby permitting rapid diagnosis of potential sites of EM failure early in the IC design and fabrication process, and thereby allowing more rapid development of reliable ICs robust against EM failure. Specific results for EM failure criteria in Cu interconnects are also presented.
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Citations
20 Claims
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1. A method for improving the design of integrated circuits (ICs) by improving resistance to electromigration failure, the method comprising:
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for a candidate IC design, varying current density j and interconnect length L through a range of values for each interconnect and, at each set of values, determining a lifetime until electromigration failure with a Technology Computer Aided Design (TCAD) computer simulation; and
,constructing one or more charts of lifetime as functions of j and L; and
,extracting from these one or more charts, one or more regions of safety from electromigration failure, one or more electromigration failure regions, and one or more aware regions of neither safety nor failure; and
,correlating the safety, failure, and aware regions with ranges of the product jL; and
,determining susceptibility to electromigration failure for interconnects within the integrated circuit by computing the product jL for each interconnect and determining if it falls in a safe, failure, or aware region, and redesigning the IC for those interconnects in the failure region so as to move the jL product out of the failure region. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method for the determination of electromigration performance of Cu interconnect sites within an integrated circuit, the method comprising:
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computing the product of current density, j, and interconnect length, L, for the interconnects within the integrated circuit; and
,identifying interconnects prone to electromigration failure as those interconnects for which the jL product is greater than about 9,000 amps/cm. - View Dependent Claims (10)
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11. A method for improving the design of an integrated circuit (IC) by improving the electromigration failure lifetime (tf) wherein the IC contains at least one interconnect and barrier layer, the method comprising:
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a) performing a sensitivity analyses on tf with a sequence of Technology Computer Aided Design (TCAD) computer simulations for material properties of the interconnect and barrier layer, thereby determining the sensitivity of tf to the material properties wherein the sensitivity analysis comprises; a-1) choosing a value for initial vacancy concentration (IVC) as the estimated value of the oxygen concentration directly beneath the barrier layer; and
,a-2) choosing a value for void formation density (VFD) as the estimated value of the metal segregation concentration; and
,a-4) performing a TCAD sensitivity analysis on tf to determine the sensitivity of tf to IVC, VFD; and
,b) setting Gibbs free energy parameter values for the surface energy density (SED) and grain boundary surface energy density of voids (GED); and
,c) determining with TCAD computer simulation the dependence of tf on the length L of a particular interconnect under consideration, and determining the range of material properties relatively safe from electromigration failure, by the following steps (c-1)-(c-4); c-1) determining tf for a sequence of L values and for a sequence of current densities (j); and
,c-2) determining safe and failure regions from the results of (c-1) and an aware region between the safe region and the failure region; and
,c-3) determining values of the jL product at the boundaries of the safe and failure regions; and
,c-4) performing further TCAD computer simulations in the tf aware region; and
,d) determining the dependence of tf on temperature (T) to determine safe temperature regions by the following steps (d-1)-(d-3); d-1) determining activation energies associated with the diffusion process from an Arrhenius plot of tf under forward and reverse current flows; and
,d-2) determining the temperature dependence of tf under the condition that the void concentration (Cvoid) is substantially the same as the vacancy concentration (Cv); and
,d-3) determining the temperature dependence of the Blech threshold (jL)c in the aware region; and
,e) comparing the tf values determined herein with measured values of tf; and
,f) returning to step (b) if the value tf values determined herein differ from the measured tf values by more than a desired amount, otherwise terminate the method and record the material property values that produced adequate agreement; and
,g) employing the material properties producing good agreement between computed tf and measured tf, identifying interconnects susceptible to electromigration failure; and
,h) redesigning the IC so as to increase tf for those interconnects susceptible to electromigration failure, thereby increasing the robustness of the IC. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification