High-accuracy physical modeling of submicrometer MOSFET's

When short-channel MOSFET transistor models are compared to experimental data, the uncertainty in some of the physical input variables often requires that some of the input variables be adjusted to fit the data. This uncertainty is increased by a lack of knowledge of process sensitivity information on critical parameters. These uncertainties have been eliminated using a two-dimensional finite-element model of a MOSFET with no free parameters. The model is compared to four self-aligned silicon-gate n-channel MOSFET's with channel lengths of 0.80, 1.83, 2.19, and 8.17 µm. The 0.80, 1.83, and 8.17-µm devices have phosphorus sources and drains. The 2.19-µm device has an arsenic source and drain. These devices span the range of channel lengths from a short-channel device, totally dominated by velocity saturation and source-drain profile shape, to a long-channel device, well characterized by a long-channel model. Using the data obtained from the measurements described in this work, it is possible to model the drain current for all of the transistors studied without adjustable parameters. Transistors with 0.80-µm channel length differ in model input from those with 8.17-µm channel length only in the length of the polysilicon gate. If sufficiently accurate parameters are available, these methods allow the characteristics of submicrometer transistors to be predicted with ±5-percent accuracy. These simulations show that the observed short-channel effects can be accounted for by existing mobility data and a simple empirical model of these data. Triode and saturation effects are dominated by two-dimensional drain field penetration of the channel region. Subthreshold effects are caused by distortion of fields in the entire channel region by the drain field.