Early Failure Mode Research Articles

Large-Scale Electromigration Statistics for Cu Interconnects

AbstractEven after the successful introduction of Cu-based metallization, the electromigration failure risk has remained one of the important reliability concerns for advanced process technologies. The observation of strong bimodality for the electron up-flow direction in dual-inlaid Cu interconnects has added complexity, but is now widely accepted. More recently, bimodality has been reported also in down-flow electromigration, leading to very short lifetimes due to small, slit-shaped voids under vias. For a more thorough investigation of these early failure phenomena, specific test structures were designed based on the Wheatstone Bridge technique. The use of these structures enabled an increase of the tested sample size past 1.1 million, allowing a direct analysis of electromigration failure mechanisms at the single-digit ppm regime. Results indicate that down-flow electromigration exhibits bimodality at very small percentage levels, not readily identifiable with standard testing methods. The activation energy for the down-flow early failure mechanism was determined to be 0.83 ± 0.01 eV. Within the small error bounds of this large-scale statistical experiment, this value is deemed to be significantly lower than the usually reported activation energy of 0.90 eV for electromigration-induced diffusion along Cu/SiCN interfaces. Due to the advantages of the Wheatstone Bridge technique, we were also able to expand the experimental temperature range down to 150 °C, coming quite close to typical operating conditions up to 125 °C. As a result of the lowered activation energy, we conclude that the down-flow early failure mode may control the chip lifetime at operating conditions. The slit-like character of the early failure void morphology also raises concerns about the validity of the Blech-effect for this mechanism. A very small amount of Cu depletion may cause failure even before a stress gradient is established. We therefore conducted large-scale statistical experiments close to the critical current density-length product (jL)*. The results indicate that even at very small failure percentages, this critical product seems to extrapolate to about 2900 ± 400 A/cm for SiCOH-based dielectrics, close to previously determined (jL)* products of about 3000 ± 500 A/cm for the same technology node and dielectric material, acquired with single link interconnects. More detailed studies are currently ongoing to verify the extrapolation methods at small percentages. Furthermore, the scaling behavior of the early failure population was investigated.

A Robust Multilevel Interconnect Module for Subquartermicrometer Complementary Metal Oxide Semiconductor Technology Integration

In this work, we present detailed studies of two integration schemes for an aluminum-wire/tungsten-plug-based multilevel ultralarge scale integration (ULSI) interconnect module for subquartermicrometer complementary metal oxide semiconductor (CMOS) technologies, and discuss the benefits and drawbacks of each of them primarily from a process integration point of view. We demonstrate that an etch stop (ES) integration scheme in which the via etch stops on the TiN cladding layer could result in significantly improved via electromigration performance compared to an over etch (OE) integration scheme in which the via is overetched into the underlying Al(Cu). We also identified several highly detrimental early failure modes associated with the OE structure, including contamination-induced stress void formation underneath the via, the metal extrusion inside the via, and the metal corrosion at the bottom of the via, and showed that such early failure modes could be prevented in the ES integration scheme. Even though there were some small penalties in the device performance in the ES integration scheme, the benefits in the reliability and the better tolerance to manufacturing process variation clearly justify the adoption of this robust multilevel ULSI interconnect module for subquartermicrometer CMOS technologies. © 2002 The Electrochemical Society. All rights reserved.

Early failure analysis of machining centers: a case study

Abstract To eliminate the early failures and improve the reliability, nine ex-factory machining centers are traced under field conditions in workshops. Their early failure information throughout the ex-factory run-in test is collected. The field early failure database is constructed based on the collection of field early failure data and the codification of data. Early failure mode and effects analysis is performed to indicate the weak subsystem of a machining center or the troublemaker. The distribution of the time between early failures is analyzed and the optimal ex-factory run-in test time for machining center that may expose sufficiently the early failures and cost minimum is discussed. Suggestions how to arrange ex-factory run-in test and how to take actions to reduce early failures for machining center is proposed.

粉末プロセスの制御と製品評価 Ｎｉ内部電極積層セラミックコンデンサのＩＲ加速寿命に及ぼす材料混合度の影響

The effect of the mixing procedure of dielectric materials on electrical Properties for multilayer ceramic capacitors(MLCCs) with Ni-electrode has been studied. When mixing is not enough, the fraction defective of insulation resistance is high and the failure mode of accelerated life of insulation resistance show two types (early failure mode and wear-out failure mode). As a result of analysis, segregated phase of small amount of ingredients was detected at the defective spot. These segregated phases resulted from lack in mixing of dielectric materials. It is concluded that highly reliable MLCCs with Ni-electrode are achieved by controlling the mixing procedure of dielectric materials.

Bimodal lifetime distributions of dielectrics for integrated circuits

Constant voltage stressing of large area capacitors with thin thermal oxide and ONO dielectrics reveals that defect related breakdown is the dominant failure mode. Elimination of the complete early failure mode by means of screening will neither be possible nor necessary. Consequently, prediction of failure rates under operating conditions must be deduced from defect-related distributions. A statistical model is introduced and discussed in order to extrapolate to small failure percentages. Furthermore an additional term is introduced in the effective thickness model of Lee et al. which takes into account the weaker field acceleration behaviour of very thin dielectrics.

The effects of screening on the reliability of GaAlAs/GaAs semiconductor lasers

The effects of a two-stage test method on the reliability assurance of GaAlAs/GaAs lasers are examined. Life-test data indicate that early failure mode can be effectively eliminated by a prelife-test screening procedure. Degradation rates obtained after removing these prematurely failured devices provide a useful parameter to predict device lifetime statistically. However, another degradation mode, developed during laser lifetime, prevents the use of this degradation rate to calculate realistic individual device lifetimes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ion Propulsion Flight Experience, Life Tests, and Reliability Estimates

The application of low-thrust ion propulsion systems to space missions requires long duration (~ 5,000-20,000 hr) component operation. Thus, components must be developed with wearout mean times to failure in excess of these required mission times. Furthermore, chance failures which occur during the useful life of components must be minimized. This paper makes an assessment of both early and wearout failure modes of ion propulsion systems by examining the results of existing developmental and long duration testing. Estimates of chance failure rates of system components are also presented along with design concepts which maximize total propulsion system reliability. I. Introduction B ECAUSE of the long time operation required for most space applications, ion propulsion system reliability is a major concern. For this reason, the long duration and space testing of critical components, subsystems, and systems associated with primary and auxiliary ion propulsion systems are of great importance. It should be recognized, however, that although a large number of long duration tests have been conducted to date on ion propulsion systems, subsystems, and components, these tests have been part of a technology development phase and are not to be considered statistical reliability testing of fully developed systems. Thus, even though space-qualified ion propulsion systems are becoming available, system reliability can only be inferred from the results of past and present developmental testing and estimated by analytical techniques.