Larry Ting

Formation and suppression of a newly discovered secondary EOS event in HBM test systems

A previously undetected trailing pulse from HBM testers was found to create unexpected gate oxide failures on new technologies. This secondary pulse, which is EOS in nature, is caused by the discharge relay and the parasitics of the charge circuit. This paper investigates this critical phenomenon and establishes the tester improvements to safely suppress the trailing pulse effects.

Process Integration Of Low-Dielectric-Constant Materials

As device geometries and operating voltage continue to scale while functional density increases, it is imperative to reduce the RC time delay. The replacement of Si0 2 as an intermetal dielectric with an insulator of lower dielectric constant is a particularly attractive solution since it provides immediate performance improvement through reduction in capacitance. An embedded polymer integration scheme improves the interconnect performance through line-to-line capacitance reduction by using polymer only between tightly spaced lines. The gapfill polymeric materials do not degrade the electromigration performance of standard multilayered TiN/Al/TiN interconnects. Embedded polymers alleviate many of the integration and reliability problems associated with polymer integration, and can be easily adopted into a standard production process.

Reduction in flux divergence at vias for improved electromigration in multilayered AlCu interconnects

Using of W‐plug vias in AlCu interconnects is known to significantly degrade electromigration (EM) performance because W is a diffusion barrier and prevents the depleting species by EM from being replenished at the via. In the present study, we demonstrate that this problem of limited source for EM migrating species can be dramatically alleviated in a multilayered metallization of TiN/AlCu/TiN using Al‐plug vias. EM lifetime improvements as large as by an order of magnitude are accomplished by reducing the flux divergence at the Al‐plug via. This flux divergence is critically determined by the effective thickness of some transition metal films at the via, which include a Ti/TiN stack for the via barrier and a TiN layer of antireflection coating for the bottom level metal lead. Scanning electron microscopy failure analysis also verifies that the samples with W‐plug vias have the void damages consistently located at the via. For the samples with Al‐plug vias and with the flux divergence at the via being lar...

Implementation of low-dielectric-constant materials for ULSI circuit performance improvement

As device geometries and operating voltage continue to decrease while functional density increases, it is imperative to reduce the RC time delay. The new embedded polymer structures improves the interconnect performance through line-to-line capacitance reduction by using polymer only between tightly spaced lines. The gapfill polymeric materials do not degrade the electromigration performance of standard multilayered TiN-Al-TiN interconnects. This scheme alleviates many of the integration and reliability problems associated with polymers, and can be easily adopted into a standard production process.

Designing and Building Reliability Into VLSI Interconnect Systems

The optimization of electromigration (EM) and stress-induced voiding (SV) properties of advanced interconnects impacts many critical system design parameters. In particular, the choice of materials and manufacturing processes must be carefully planned during the early phases of product development. In layered metallizations, both the barrier and capping layers design can affect electromigration resistance and stress-relaxation behavior, while electrical performance often constitutes a trade-off. This is shown specifically in a study of titanium diffusion into Al-Cu from TiN barrier layers, and in initial stress-relaxation tests characterizing the effect of Ti addition in the capping layer. The development of advanced characterization techniques supports the trial-and-error experimental optimization process, but models predicting EM and SV reliability are needed and should include complex sets of microstructural and design parameters.

Effect of heat treatments on electromigration performance for TiN/AlCu/TiN interconnect

The thermal stability of multilayered TiN/AlCu/TiN interconnect metallization and its impact on electromigration reliability performance has been investigated. Upon heat treatments at 450 degree(s)C, a monotonic increase in sheet resistance of the metal structure was observed. The test results on samples with different structures, including single-layered AlCu, AlCu/TiN(cap), TiN(bottom)/AlCu, and TiN(bottom)/AlCu/TiN(cap), showed that the sheet resistance increase due to heat treatment effect occurred only for the last two structures which had a TiN barrier. This indicates that the observed sheet resistance increase resulted from occurrence of some intermetallic reactions between AlCu and the underlying TiN barrier, but similar reactions did not occur between AlCu and the TiN in the capping layer. The result was further verified by cross sectional TEM and RBS analysis on samples with heat treatments. The heat treatment effect on electromigration performance was found to be significant leading to lifetime variations over an order of magnitude. A bell-shaped relationship between electromigration lifetime and the metal sheet resistance was found on samples receiving varying cycles of heat treatments. The observed effect is believed to be due to doping effect of Ti diffusing from the underlying TiN barrier into AlCu. It is concluded that a good control over the cumulative thermal budget is essential to assure electromigration reliability for TiN/AlCu/TiN metallizations, which is especially critical for multilevel metallizations.