Ibrahim Avci

Efficient TCAD Model for the Evolution of Interstitial Clusters, {311} Defects, and Dislocation Loops in Silicon

The simulation of deep-submicron silicon-device manufacturing processes relies on predictive models for extended defect clusters. For submicroscopic interstitial clusters and {311} defects, an efficient and highly accurate model for process simulation has been developed and calibrated recently [1]. This model combines equations for three small interstitial clusters and two moments for {311} defects. In this work, we extend this model to include dislocation loops and to reproduce a greatly increased range of experimental data, including thermal annealing of end-of-range defects after amorphizing implants.

A numerical model using the phase field method for stress induced voiding in a metal line during thermal bake

We present a numerical model using the phase-field method (PFM) for stress-induced-voiding (SIV) in a metal line. The model was verified by comparison with the typical stress-migration (SM) analytical model. We investigated the effects of flaw location and density on time-to-failure (TTF). The model was applied to the failure analysis of the BEOL process of a 0.13um device for automobiles.

Investigation of Proximity Effects in a 6T SRAM Cell Using Three-Dimensional TCAD Simulations

In this paper, we study the impacts of proximity effects on the electrical characteristics Id-Vg and the static noise margin of a six-transistor (6T) bulk complementary metal-oxide-semiconductor (MOS) static random access memory (SRAM) cell using 3-D process and device technology computer-aided design (TCAD) simulations. We show that when a 6T SRAM cell is simulated as a single continuous 3-D structure, effective stresses in channels are reduced due to close proximity of n-channel and p-channel MOS transistors in the cell with respect to simulations of transistors as discrete 3-D structures. Furthermore, we find that doping in channels of SRAM transistors is reduced by well proximity and implant shadowing. Stress and doping proximity effects have opposite contributions to device performance. We estimate the influence of proximity effects for typical 32-nm technology to be more than 10% for certain electrical cell characteristics. We thus conclude that, to accurately predict electrical cell behavior via TCAD simulations, the 6T SRAM cell should be a single continuous 3-D structure, instead of a set of six discrete transistors, which are simulated as individual 3-D devices and connected via a netlist.

Reliability analysis of bumping schemes under chip package interaction

Reliability analysis for three bumping configurations is performed under typical chip package interaction. A sequential submodeling technique is employed to capture stress evolution during entire package assembly process. Mechanical stresses are assessed in various regions around bumps to determine the optimal bumping scheme with the minimal reliability risk. Underfill material property impact on package reliability is also examined. This study provides important guidelines to design robust bumping configurations with fine-tuned material properties.

Determination of Cu-line EM Lifetime Criteria Using Physically Based TCAD simulations

A physically based simulation methodology provides fast and practical EM lifetime prediction. We identified an “EM-aware” region to define the length dependence of Cu-lines under high current stress. For eventual calibration of 2× nm node Cu-lines, we analyzed the sensitivity trends of vacancy and void profiles as well as the mass transport mechanisms using a 3D TCAD tool. This includes electron flow dependency to explain line and via depletion effects for void formations under various EM stress conditions. We report a non-linearity in the length dependence on the EM failure jL product at ~9000 A/cm and a slight temperature dependence on the Blech Threshold (jL)c at ~2000 A/cm extracted at 300°C in the EM aware region.

Computational analysis of mechanical and electromigration reliability problems

The reliability of complex interconnect structures at all levels of the chip integration hierarchy has become a major concern due to the use of fine feature sizes, diverse materials, and complex 3D architectures. Reliability issues range from stress related failures such as dielectric cracking and interface debonding during manufacturing to electrical and mechanical failures such as electromigration and void formation during operation. This paper summarizes computational results obtained using a unified physics-based 3D simulation framework.

Three-dimensional TCAD Process and Device Simulations

Shrinking feature sizes, novel device designs as well as stress engineering increase the need for three- dimensional process and device simulations. We present several application examples for full 3D process and device simulations using Sentaurus TCAD, including a 3D NMOSFET with shallow trench isolations (STI), a PMOSFET device with SiGe pockets for stress engineering (similar to the structure presented in Ref. [1]) and a Omega-FinFET (similar to structures presented in Refs. [2,3]). TCAD simulations of the full process flow as well as of the electrical device characteristics are performed. We also show examples of 3D oxidation simulations with Sentaurus Process.

From point defects to dislocation loops: A comprehensive TCAD model for self-interstitial defects in silicon

An atomistic model for self-interstitial extended defects is presented in this work. Using a limited set of assumptions about the shape and emission frequency of extended defects, and taking as parameters the interstitial binding energies of extended defects versus their size, this model is able to predict a wide variety of experimental results. The model accounts for the whole extended defect evolution, from the initial small irregular clusters to the {311} defects and to the more stable dislocation loops. The model predicts the extended defect dissolution, supersaturation and defect size evolution with time, and it takes into account the thermally activated transformation of {311} defects into dislocation. The model is also used to explore a two-phase exponential decay observed in the dissolution of {311} defects.