Polysilicon gate with depletion - or - metallic gate with buried channel : what evil worse ? E.Jossel and T.Skotnicki"* 'France Telecom, CNET Grenoble, 38243 Meylan, France. Ph: +(33) 4 76764591, Fax: +(33) 4 76764063 2STMicroelectronics,850 rue Jean Monnet, 38291 Crolles, France. e-mai1:
[email protected] Unfortunately, gate polydepletion, defined as the relative shift in gate capacitance with respect to metallic gate will increase Metallic gates are expected to overcome polysilicon's limitations, such as polydepletion. Nevertheless, this option (Fig.2) since tox is reduced. Our experiments with both must be associated with buried channel to ensure low VTH PMOS and nMOS (also plotted in Fig.2) show that operation. Taking into account realistic projections on polydepletion is always more pronounced at PMOS side. The technological capabilities, such as active gate doping, oxide interfacial gate doping extracted from the data in Fig.2 ' ~ 1x102' cms3for PMOS and nMOS, thickness or junction depth, we confirm that the degradation saturates at 6 ~ 1 0 and in performances due to the buried channel is definitively respectively. Moreover, the use of Boron as a gate dopant is governed by the trade-off between depletion and penetration much more restrictive than that relative to the polydepletion. through oxide. To improve this trade-off, promising options such as poly-SiGe (to enhance Boron activation [l-4]), or Introduction fine-grain columnar poly-Si (to get better drive-in and As MOSFETs are scaled down to 0.1 pm and below, ultra- distribution at the interface [4,5]) can constitute low cost thin gate oxides are needed to keep high drive performance alternatives to amorphous Si. Using fine-grain columnar polyand to control short channel effects (SCE).Unfortunately, Si with a medium thermal budget process (
