DGO Formation by Lateral Oxidation
Original Publication Date: 2002-Jul-15
Included in the Prior Art Database: 2002-Jul-15
Silicon dioxide (SiO2) has been the MOSFET gate dielectric of choice over other dielectrics because of its physical and electrical properties. However, as MOSFET dimensions are scaled, the gate leakage current becomes unacceptably high when the SiO2 is scaled to a thickness range where direct tunneling is the primary conduction mechanism. To achieve a lower leakage current at the same equivalent oxide thickness (EOT), the SiO2 can be replaced with a thicker dielectric that has a higher permittivity. Metal oxide insulators such as zirconium dioxide (ZrO2) and hafnium dioxide (HfO2) are examples of two dielectrics with permittivities higher than SiO2. To form a metal oxide with an extremely low electrical oxide thickness (tox), it is extremely important to control the surface preparation. The ability to scale down the thickness of a metal oxide will be limited by the quality and thickness of any surface oxide or pretreatment. Thus it is desirable to remove the native oxide on the surface prior to formation of the metal oxide gate dielectric. Two methods for removing a native oxide are HF cleaning and hydrogen baking at elevated temperatures. On a chip, it is desirable to have MOSFETs with different gate dielectric thickness to address the needs for high and low voltage operation. A thin gate dielectric is used for the high performance device that is operated using low voltages whereas a thicker gate dielectric is used for MOSFETs that are operated using high voltages. The presence of two such different dielectrics is referred to as a Dual Gate Oxide (DGO).