Effects of thermal stress induced by mulitiple through silicon vias on mobility and keep out zone

Abstract

Effects of thermal stress induced by multiple through silicon vias (TSVs) on mobility and keep out zone (KOZ) are mainly discussed in this paper. It is found that the angle and pitch between TSVs have a great effect on the carrier mobility and KOZ. In this paper, the device channel direction is set along [100]. And two types of KOZ are presented, namely the variations of electron mobility are 5% and 10% respectively. As for the two TSVs, their KOZ sizes change significantly with the angles between TSVs which change from zero to π/4, and the area of a KOZ is the minimum when the angle is π/4. But the zone for device placement is irregular, which is difficult for agreement. The area of a KOZ is the maximum when the angle is zero, and it is easy to make arrangement as the space for device distribution is regular. Based on these analyses, the effects of pitch between TSVs are presented. When the angle is zero, the area of KOZ decreases as the pitch increases and tends to be the same as that of a single TSV. For example, the KOZ, in which the variations of electron mobility are 5% and 10%, will reduce to 8.4 μm and 5.1 μm as the pitch increases to 20 μm, which is close to that of the single TSV. But when the angle is π/4, the KOZ with an electron mobility 5% increases from 5.2 to 6.4 μm as the pitch increases and tends to be the same as that of a single TSV at last. The KOZ with an electron mobility 10% will increase from 4.2 to 4.5 μm. In addition, the above analyses can be extended to the KOE of four TSVs, a more representative pattern. And two kinds of TSV displacement style including “square” and "diamond" TSV patterns are also discussed, the impact of pitch for these two patterns are also given in this paper. For the “square” TSV pattern, the KOZ decreases as the pitch increases. Under this condition, the devices can only be placed in a small square region surrounded by TSVs, but the region is regular, which is beneficial for device arranging. While for the "diamond" TSV pattern, the KOZ increases as the pitch increases. Under this condition, the area for device placement is larger than the “square” TSV pattern, but the region is irregular as it is divided into long narrow parts, which is hard for device placement.