MOS Scaling: Transistor Challenges for the 21st Century

Conventional scaling of gate oxide thickness, source/drain extension (SDE), junction depths, and gate lengths have enabled MOS gate dimensions to be reduced from 10mm in the 1970’s to a present day size of 0.1mm. To enable transistor scaling into the 21st century, new solutions such as high dielectric constant materials for gate insulation and shallow, ultra low resistivity junctions need to be developed. In this paper, for the first time, key scaling limits are quantified for MOS transistors (see Table 1). We show that traditional SiO2 gate dielectrics will reach fundamental leakage limits, due to tunneling, for an effective electrical thickness below 2.3 nm. Experimental data and simulations are used to show that although conventional scaling of junction depths is still possible, increased resistance for junction depths below 30 nm results in performance degradation. Because of these limits, it will not be possible to further improve short channel effects. This will result in either unacceptable off-state leakage currents or strongly degraded device performance for gate lengths below 0.10mm. MOS transistor limits will be reached for 0.13mm process technologies in production during 2002. Because of these problems, new solutions will need to be developed for continued transistor scaling. We discuss some of the proposed solutions including high dielectric constant gate materials and alternate device architectures.