Distinguishing Between STI Stress and Delta Width in Gate Direct Tunneling Current of Narrow n-MOSFETs

Direct tunneling current across a 1.27-nm-thick gate oxide of n-MOSFETs under STI compressive stress is measured in a wide range of the drawn gate width W( = 0.11, 0.24, 0.6, 1.0 and 10 mum). The apparent gate current per unit width exhibits an increasing trend with decreasing W. In this narrowing direction, two fundamentally different effects are encountered: one of the delta width (DeltaW) near the STI edge, and the other of the enhanced STI stress in the channel. To distinguish between the two effects, a new analytical width-dependent direct tunneling model is developed and applied. Reasonable agreement with data is achieved. The resulting delta width effect is found to dominate over the stress effect in narrow devices, while for the wide ones, they are comparable. The extracted DeltaW( ~ 63 nm) and the underlying channel stress (with the uncertainties identified) straightforwardly produce a good fitting of the drain current variation counterpart. Specifically, it is justified that the delta width and STI stress are cooperative in constituting gate current variation, but both have opposite effects on the drain current one.