Hans-Jürgen Engelmann

Effect of interface strength on electromigration-induced inlaid copper interconnect degradation: Experiment and simulation

Abstract Both in situ microscopy experiments at embedded inlaid copper interconnect structures and numerical simulations based on a physical model provide information about electromigration-induced degradation mechanisms in on-chip interconnects. It is shown that the modification of the bonding strength of the weakest interface results in completely changed degradation and failure mechanisms. Transmission electron microscopy (TEM) images of standard Cu/SiNx interfaces are compared with strengthened interfaces, e. g., after applying an additional metal coating or a self-assembled monolayer (SAM) on top of the polished copper lines. The changed degradation mechanisms as observed with the in situ scanning electron microscopy (SEM) experiment and as predicted based on the numerical simulations are explained based on TEM images.

Improving accuracy and precision of strain analysis by energy-filtered nanobeam electron diffraction.

This article deals with uncertainty in the analysis of strain in silicon nanoscale structures and devices using nanobeam electron diffraction (NBED). Specimen and instrument related errors and instabilities and their effects on NBED analysis are addressed using a nanopatterned ultrathin strained silicon layer directly on oxide as a model system. We demonstrate that zero-loss filtering significantly improves the NBED precision by decreasing the diffuse background in the diffraction patterns. To minimize the systematic deviations the acquired data were verified through a reliability test and then calibrated. Furthermore, the effect of strain relaxation by specimen preparation using a FIB is estimated by comparing profiles, which were acquired by analyzing slices of strained structures in a 220-nm-thick region of the sample (invasive preparation) and the entire strained nanostructures, which are embedded in a thicker region of the same sample (noninvasive preparation). Together with the random deviation, the corresponding systematic shift results in a total deviation of ∼1 × 10(-3) for NBED analyses, which is employed to estimate the measurement uncertainty in the thinner sample region. In contrast, the strain in the thick sample region is not affected by the preparation; the systematic shift reduces to a minimum, which improves the total deviation by ∼50%.

CPI assessment using a novel characterization technique based on bump-assisted scratch-indentation testing

Integration of compliant and brittle ultralow-k (ULK) interlayer dielectric (ILD) materials in advanced backend-of-line (BEOL) layer stacks requires a careful characterization of the mechanical stability of the BEOL stack to assure reliability during chip packaging and under field condition. We present a novel experimental technique which applies normal and shear forces on Cu pillars to test the stability of BEOL layer stacks beneath individual pillars. Critical forces and displacements are recorded with high sensitivity. The test directly verifies if the BEOL withstands the applied stress levels or if mechanical failure occurs.

An experimental methodology for the in-situ observation of the time-dependent dielectric breakdown mechanism in Copper/low-k on-chip interconnect structures

This study captures the time-dependent dielectric breakdown kinetics in nanoscale Cu/low-k interconnect structures, applying in-situ transmission electron microscopy (TEM) imaging and post-mortem electron spectroscopic imaging (ESI). A “tip-to-tip” test structure and an experimental methodology were established to observe the localized damage mechanisms under a constant voltage stress as a function of time. In an interconnect structure with partly breached barriers, in-situ TEM imaging shows Cu nanoparticle formation, agglomeration and movement in porous organosilicate glasses. In a flawless interconnect structure, in-situ TEM imaging and ESI mapping show close to no evidence of Cu diffusion in the TDDB process. From the ESI mapping, only a narrow Cu trace is found at the SiCN/OSG interface. In both cases, when barriers are breached or still intact, the initial damage is observed at the top interface of M1 between SiCN and OSG.

Small grain and twin characterization in sub-100 nm Cu interconnects using the conical dark-field technique in the transmission electron microscope

The introduction of future technology nodes is accompanied by further downscaling of the interconnect dimensions resulting in the growth of Cu grains with a grain size that is significantly smaller than 100 nm. Consequently, well established techniques for orientation imaging microscopy reach their resolution limit for sufficient Cu microstructure characterization. The only suitable alternative is given by transmission electron microscopy, and particularly, by applying the conical dark-field (CDF) technique which provides complete grain orientation maps. With a proven spatial resolution of better than 5 nm, various interconnect structures with Cu twins and agglomerates of small Cu grains are analyzed by the CDF technique.

Conical Dark‐Field Analysis For Small Grain Characterization In Narrow Cu Interconnect Structures: Potential And Challenges

Conical dark‐field (CDF) analysis in the transmission electron microscope is introduced as a suitable method for characterizing small Cu grains in advanced interconnect structures. With a proven spatial resolution in the <5 nm range, the CDF technique is not only applied for monitoring the microstructure of Cu interconnect lines during process development and control, but also for Cu grain orientation determination in conjunction with electromigration and stress‐migration experiments to study the influence of Cu microstructure on reliability‐limiting degradation processes. To obtain accurate orientation information with high lateral resolution, several challenges associated with data acquisition and subsequent data analysis have to be accomplished. Besides a well‐aligned microscope and stable measuring conditions, a suitable choice of the evaluation parameters and appropriate handling of diffraction pattern superposition are crucial for reliable Cu orientation determination.

New failure mechanism during high temperature storage testing and its application on SIV risk evaluation

In this paper we showed results on high temperature storage tests performed on 90nm, 65nm and 45nm node material with different back end of line stacks. We have seen a strong impact of BEOL stack up on resistance traces of tests at temperature of over 250°C for 1000h. We found that the detected resistance increases are not related to stress migration phenomena but to changes in barrier integrity. The results suggest that the barrier is oxidizing due to oxygen supplied by the SiCOH ILD. First look into future technologies by adopted barrier processes simulating corresponding barrier thicknesses we see an acceleration of this results. Porous SiCOH which is used as baseline material for 45nm an beyond is even pronouncing this effect. This is definitely showing that this effect might become severe in future technologies.

FIB-Präparation und TEM-Analytik an AlSi1-Bondkontakten

Kurzfassung Bei der Untersuchung der Verbindungsbildung von Bondkontakten sehr geringer Ausdehnung (25 μm-AlSi1-Draht auf Cu/Ni/Au-Metallisierung einer Leiterplatte) steht mit der Methode des Fokusierten Ionenstrahles (FIB) für die TEM-Zielpräparation ein sehr effektives Verfahren zur Verfügung, das die genaue Entnahme einer Lamelle aus dem interessierenden Probenbereich ermöglicht. Dabei gelingt es mit dem in-situ-lift-out-Verfahren im Vergleich zum ex-situ-lift-out-Verfahren dünnere Folien zu präparieren (ca. 40 nm), an denen im Bereich der Grenzfläche zwischen Bonddraht und dem Metallisierungschichtsystem EFTEM-Mappings und HRTEM-Untersuchungen möglich werden. Diese Untersuchungen liefern zusammen mit der Anwendung des FIB als Rasterionenmikroskop neue Erkenntnisse zum Gefüge der Bondkontakte und zum Aufbau der Grenzfläche und erweitern das Verständnis der Verbindungsbildung beim Drahtbonden.

Elemental mapping of multilayered structures: A method to reconstruct 2D chemical maps from a set of 1D line scans

We introduce a method to characterize the chemical distribution in nanostructures using STEM and affiliated spectroscopy techniques. The method is applicable to any nanostructure where the continuous layers of arbitrary geometry and dimensions can be identified. The key feature of the suggested approach is digital warping of the original STEM image into the quasi-1D image. The chemical profiles of high resolution and high signal-to-noise ratio can be extracted from the minimal set of the STEM spectroscopy data while minimizing material damage during acquisitions. Finally, the 2D chemical maps of the area of interest are reconstructed.