Lionel Cadix

Modelling of Through Silicon Via RF performance and impact on signal transmission in 3D integrated circuits

Through Silicon Via (TSV) is considered today as the third dimension interconnect opening new perspectives in term of 3D integration. Design, material and process recommendations are required to achieve 3D stacked dies and evaluate electrical performance of such chips. As a consequence, equivalent models of this incontrovertible key component become more and more mandatory. In this paper, a full parametric and frequency dependent model of high aspect ratio TSV is proposed based on both electromagnetic (EM) simulations and RF measurements. This model enables to extract TSV resistance, self inductance, oxide capacitance and parasitic elements due to the finite substrate resistivity. Its full compatibility with SPICE solvers allows the investigation of TSV impact on circuit performance.

First integration of Cu TSV using die-to-wafer direct bonding and planarization

Copper-filled Through-Si Vias (TSV) with diameters from 2 µm to 5 µm have been integrated in a die-to-wafer stack combining direct bonding and a planarization technique. TSVs were processed on chip backside after oxide bonding and substrate thinning. The results were compared to the ones achieved with a wafer-to-wafer test vehicle. It was demonstrated that die-to-wafer process developed for this integration does not impact TSV electrical and morphological properties. Moreover, no damage was observed on the stack during TSV process performed at 400°C. This demonstration is the first step to validate the industrial compatibility between high density TSV process and die-to-wafer direct bonding and planarization techniques. With a resistance close to 150 mOhm and a capacitance of about 30 fF, 3 µm-diameter TSV provides excellent electrical performance to heterogeneous 3D ICs.

Integration and frequency dependent parametric modeling of Through Silicon Via involved in high density 3D chip stacking

Evaluation of Through Silicon Via (TSV) electrical performance is hardly required today to improve heterogeneous 3D chip performance in the frame of a “more than Moore” approach. Accurate modeling of TSV is consequently essential to perform design optimizations and process tuning. This paper proposes a methodology based on RF characterizations and simulations, leading to a frequency dependent analytical model including MOS effect of high aspect ratio TSV. Specific test structures integrated on both floating Si bulk and CMOS 65 nm active wafers according to a face-to-face Via Last After Bonding process enable C(V) and RF measurements. TSV equivalent model including all substrate effects is proposed according to CMOS 65 nm specificities (voltage, frequency, dimensions and Si conductivity) and implemented in SPICE simulator to predict TSV impact on signal propagation.