Ritwik Chatterjee

Failure mechanisms and optimum design for electroplated copper Through-Silicon Vias (TSV)

Through-Silicon Vias (TSVs) have garnered a lot of interest in recent years because TSV is a key enabling technology for three dimensional (3D) Integrated Circuit (IC) stacking, silicon interposer technology, and advanced wafer level packaging (WLP). There has been significant effort in TSV fabrication and electrical design. However, considerably less work has been done on thermo-mechanical analysis and mechanical design of these structures. Due to the high coefficient of thermal expansion (CTE) mismatch between Si and the conducting material in the vias, thermo-mechanical reliability is a major concern. This paper uses Finite-Element (FE) models and X-ray diffraction (XRD) experiments for the thermo-mechanical analysis of TSVs. Two-dimensional thermo-mechanical Finite-element models have been built to analyze the stress/strain distribution in the TSV structures, and the models show that large stress gradients and plastic deformation exist near the corner of electroplated Cu pads. The stress results from the finite-element models have been compared against XRD experimental data. A fracture mechanics analysis has also been performed, and the fracture analysis shows that Cu/SiO2 interfacial cracks and SiO2 cohesive cracks are more likely to initiate and propagate at those corner locations.

Electrical modeling of Through Silicon and Package Vias

This paper presents analytical modeling and 3D full-wave electromagnetic (EM) simulation of the bias voltage dependent semiconductor (MOS) capacitance of a Through Silicon Via (TSV). An accurate electrical model of the TSV is proposed by considering the semiconductor effects. The high-frequency electrical performance of TSVs and Through-Package Vias (TPVs) are compared by means of 3D EM simulations. A parametric study is performed on TSV capacitance and design guidelines are presented for signal and power TSVs.

Analytical and Numerical Modeling of the Thermal Performance of Three-Dimensional Integrated Circuits

Three-dimensional (3D) interconnection technology offers several electrical advantages, including reduced signal delay, reduced interconnect power, and design flexibility. 3D integration relies on through-silicon vias (TSVs) and the bonding of multiple active layers to stack several die or wafers containing integrated circuits (ICs) and provide direct electrical interconnection between the stacked strata. While this approach provides several electrical benefits, it also offers significant challenges in thermal management. While some work has been done in the past in this field, a comprehensive treatment is still lacking. In the current work, analytical and finite-element models of heat transfer in stacked 3D ICs are developed. The models are used to investigate the limits of thermal feasibility of 3D electronics and to determine the improvements required in traditional packaging in order to accommodate 3D ICs. An analytical model for temperature distribution in a multidie stack with multiple heat sources is developed. The analytical model is used to extend the traditional concept of a single-valued junction-to-air thermal resistance in an IC to thermal resistance and thermal sensitivity matrices for a 3D IC. The impact of various geometric parameters and thermophysical properties on thermal performance of a 3D IC is investigated. It is shown that package and heat sink thermal resistances play a more important role in determining temperature rise compared to thermal resistances intrinsic to the multidie stack. The improvement required in package and heat sink thermal resistances for a 3D logic-on-memory implementation to be thermally feasible is quantified. An increase in maximum temperature in a 3D IC compared to an equivalent system-in-package (SiP) is predicted. This increase is found to be mainly due to the reduced chip footprint. The increased memory die temperature in case of memory-on-logic integration compared to a SiP implementation is identified to be a significant thermal management challenge in the future. The results presented in this paper may be useful in the development of thermal design guidelines for 3D ICs, which are expected to help maximize the electrical benefits of 3D technology without exacerbating thermal management issues when implemented in early-stage electrical design and layout tools.

Rigorous Electrical Modeling of Through Silicon Vias (TSVs) With MOS Capacitance Effects

3-D integration of microelectronic systems reduces the interconnect length, wiring delay, and system size, while enhancing functionality by heterogeneous integration. Through silicon via (TSV) is a key building block for high-performance 3-D systems. This paper presents an accurate electrical modeling of TSVs considering metal-oxide-semiconductor (MOS) capacitance effects. The model is correlated with measurement results for validation. Parametric analysis of TSV capacitance is performed on several physical and material parameters. Design guidelines are proposed for TSVs used in signal and power distribution networks as well as for TSVs as variable capacitors. A 3-D power distribution network is simulated to show the effect and importance of the voltage-dependent TSV MOS capacitance.

Electrical modeling and characterization of through-silicon vias (TSVs) for 3-D integrated circuits

The integration of chips in the third dimension has been explored to address various physical and system level limitations currently undermining chip performance. In this paper, we present a comprehensive analysis of the electrical properties of through silicon vias and microconnects with an emphasis on single via characteristics as well as inter-TSV capacitive and inductive coupling in the presence of either a neighboring ground tap or a grounded substrate back plane. We also analyze the impact of technology scaling on TSV electrical parasitics, and investigate the power and delay trend in 3-D interstratum IO drivers with those of global wire in 2-D circuits over various technology nodes. We estimate the global wire length necessary to produce an equivalent 3-D IO delay, a metric useful in early stage design tools for 3D floorplanning that considers the electrical characteristics of 3D connections with TSVs and microconnects.

Progress of 3D Integration Technologies and 3D Interconnects

Three dimensional stacked circuits having multiple active semiconductor levels rely on the development of strata bonding, micro connects between strata, through strata vias (TSV) and a wafer thinning process. Progress in the each of these process technologies for 3D strata stacking is opening the path to more robust and capable 3D process integrations.

Thermal modeling and design of 3D integrated circuits

3D interconnect technology has attracted significant interest in the recent past as a means for enabling faster and more efficient integrated circuits (ICs). 3D integration relies on through-silicon vias (TSVs) and bonding of multiple active layers. While this approach provides several electrical benefits, it also offers significant challenges in thermal management. While some work has been done in the past in this field, a comprehensive treatment is still lacking. In the current work, analytical and finite-element models of heat transfer in 3D electronic circuits are developed. The models are used to investigate the limits of thermal feasibility of 3D electronics and to determine the improvements required in traditional packaging in order to accommodate 3D ICs. An analytical model for temperature distribution in a multi-die stack with multiple heat sources is developed. The analytical model is used to extend the traditional concept of thermal resistance in an IC to thermal resistance and thermal sensitivity matrices for a 3D IC. The impact of various geometric parameters and thermophysical properties on thermal performance of a 3D IC is investigated. It is shown that package thermal resistances play a more important role in determining temperature rise compared to thermal resistances intrinsic to the 3D technology, including thermal resistance of bonding layers and TSVs. As a result, an improved bonding layer or TSV thermal resistance does not offer much thermal benefit. An increase in thermal resistance of a 3D IC is predicted as compared to an equivalent System-on-Chip (SoC). This increase is found to be mainly due to the reduced chip footprint. The amount of improvement required in package and heat sink thermal resistances for a logic-on-memory 3D implementation to be thermally feasible is quantified. The results presented in this paper are expected to aid in the development of thermal design guidelines for 3D ICs.

Trend from ICs to 3D ICs to 3D systems

Moores Law has driven the IC industry to a billion transistor chip. But major technical and financial barriers are foreseen beyond 32 nm. One alternative path to this challenge seems to be stacked 3D ICs. But 3D ICs are a small part of any system and the total benefits of miniaturization cannot be realized until the entire system is miniaturized. This is the basis of 3D systems, the focus of this paper. The 3D miniaturization technologies briefly described in this paper include Si or wafer level interposers with Through-Package-Vias (TPV), nano-scale passives, thermal materials and interfaces and fine pitch system interconnections.

Inter-Strata Connection Characteristics and Signal Transmission in Three-Dimensional (3D) Integration Technology

In a general case of 3D integrated circuit (IC) technology, it is desirable to design a die for 3D integration with flexibility to facilitate integration with a number of other circuit dies. We present a generic circuit technique which minimizes power consumption and circuit area while allowing reliable signal transfer between 3D dies as well as enabling the design of a bonded interface circuitry without a complete knowledge of inter-strata connection configurations. We also present parasitic RC characteristics of inter-strata connection elements, such as micro-bumps and through-substrate vias, and discuss the technology scaling trends. An inter-strata signal transmission, according to our method, has receive and transmit circuitry with programmable power supply which can be independently controlled for achieving optimum power and signal drive. In addition, the receive circuitry includes hysteresis to allow superior signal integrity in the presence of inter-strata parasitic variations

Numerical and Experimental Investigation of Thermomechanical Deformation in High-Aspect-Ratio Electroplated Through-Silicon Vias

In this paper we present the numerical and experimental analysis of thermomechanical deformation in high-aspect-ratio copper electroplated through-silicon vias (TSVs), which were fabricated by deep reactive ion etching, thermal oxidation, and bottom-up electroplating processes. Later, these TSVs were subjected to thermal cyclic loading of 25-125°C. Due to the significant mismatch in the coefficients of thermal expansion of silicon and copper, thermomechanical stress was generated at the copper-silicon interface. Detailed investigation of this stress is of prime importance as it is one of the main root-causes behind the crack formation and dielectric delamination at the interface. A three-dimensional finite element model of the copper-filled TSVs was built and simulation was performed to predict the theoretical distribution of thermomechanical deformation. A noncontact digital image speckle correlation technique was used for the in situ measurement of the thermal deformation and the thermomechanical stress. Thermomechanical shear strain at the copper-silicon oxide-silicon interface was found to be the significant deformation mode in these TSVs.