Nikolaos Minas

Design Issues and Considerations for Low-Cost 3-D TSV IC Technology

In this paper key design issues and considerations of a low-cost 3-D Cu-TSV technology are investigated. The impact of TSV on BEOL interconnect reliability is limited, no failures have been observed. The impact of TSV stress on MOS devices causes shifts, further analysis is required to understand their importance. Thermal hot spots in 3-D chip stacks cause temperature increases three times higher than in 2-D chips, necessitating a careful thermal floorplanning to avoid thermal failures. We have monitored for ESD during 3-D processing and have found no events take place, however careful further monitoring is required. The noise coupling between two tiers in a 3-D chip-stack is 20 dB lower than in a 2-D SoC, opening opportunities for increased mixed signal system performance. The impact on digital circuit performance of TSVs is accurately modeled with the presented RC model and digital gates can directly drive signals through TSVs at high speed and low power. Experimental results of a 3-D Network-on-Chip implementation demonstrate that the NoC concept can be extended from 2-D SoC to 3-D SoCs at low area (0.018 ) and power (3%) overhead.

Comprehensive analysis of the impact of single and arrays of through silicon vias induced stress on high-k / metal gate CMOS performance

As scaling becomes increasingly difficult, 3D integration has emerged as a viable alternative to achieve the requisite bandwidth and power efficiency challenges. However mechanical stress induced by the through silicon vias (TSV) is one of the key constraints in the 3D flow that must be controlled in order to preserve the integrity of front end devices. For the first time an extended and comprehensive study is given for the stress induced by single- and arrayed TSVs and its impact on both analog and digital FEOL devices and circuits. This work provides a complete experimental assessment and quantifies the stress distribution and its effect on front end devices. By using a combined experimental and theoretical approach we provide a framework that will enable stress aware design and the right definition of keep out zone and ultimately save valuable silicon area.

3D integration: Circuit design, test, and reliability challenges

3D-Stacked ICs (3D-SIC) based on Through-Silicon Vias (TSVs) offer alleviation of the performance and interconnect density bottlenecks faced by traditional CMOS scaling. As a result there is a lot of industrial focus to make this technology available for the next generation of SoCs. However, for 3D integration to become a viable product approach, it requires that the additional processing steps necessary preserve the integrity of both front-end and back-end of devices and constituting materials. 3D processing steps such as TSV insertion and wafer thinning, have an impact on the functionality and performance of analog and digital circuits, which needs to be accounted for during the design phase. Moreover, testing 3D-SICs calls for more complex test flow trade-offs and enhanced design-for-test architectures for test access within the stack. Finally, the reliability consequences with respect to thermal and mechanical stress in dense stacks of thinned wafers need to be carefully assessed to guarantee a target product life time. In this presentation we discuss the abovementioned challenges and some of the emerging solutions.

Design of Test Structures for the Characterization of Thermal–Mechanical Stress in 3D-Stacked IC

In this paper, we present test structures and measurement techniques that enable the extraction of the significance of the thermal-mechanical stress in 3D-stacked integrated circuit technology. Heaters and integrated diodes have been used to determine the impact of hotspots in 3-D systems. The results obtained showed that in 3-D case, the peak temperature of a hotspot is three times higher compared to a traditional 2-D system. For the characterization of through silicon vias (TSVs)-induced stress and its impact on analog metal-oxide semiconductor (MOS) devices, a 10-bit current steering digital-to-analog converter (DAC) test structure is utilized. The DAC has been optimized to detect ion changes down to 0.5% due to TSV proximity, TSV orientation, thermal hotspots, and wafer thinning or stacking process. The results obtained from stand-alone short-channel MOS devices and the DAC structure clearly indicate the impact of TSV proximity and TSV orientation on the carrier mobility of nearby transistors.

An efficient array structure to characterize the impact of through silicon vias on FET devices

We present a test structure to measure the impact of 3D processing, especially through silicon vias, on FET devices. We also show proven techniques for enabling large numbers of devices to be accessed from a limited number of pads. We will show that through silicon via (TSV) proximity and FET channel length impact the devices behavior. We will show behavior can be predicted by symmetry. Through measurement, analsysis, and correlation with mechanical stress models, we demonstrate that our structure can predict how FET devices will behave in 3D stacked products.

In-tier diagnosis of power domains in 3D TSV ICs

Power and substrate domains are strategically isolated or unified in heterogeneous 3D integration. In-tier probing circuitry provides accessibility to power delivery and substrate networks in a deep tier of a 3D chip stack and capability of diagnosing intra/inter tier coupling. A two-tier demonstrator was successfully tested in a 130 nm CMOS, 3D-SIC Cu TSV technology.