FABRICATION AND CHARACTERISTICS OF MIDGAP METAL GATES COMPATIBLE WITH THIN SiO_2 FILMS USING LOW PRESSURE CHEMICALLY VAPOR DEPOSITED TUNGSTEN FILMS

摘要

A process utilizing low pressure chemical vapor deposition of tungsten, dry etching and copper deposition and patterning using evaporation and liftoff was developed and used for the fabrication of tungsten gate or Cu/W gate MOS diodes, having a midgap gate work function. The characteristics of these devices, as well as the effect of thermal treatments on them, were investigated. In particular, their dielectric breakdown strength and charge trapping behavior were evaluated using Ⅰ-Ⅴ, high frequency C-V and quasistatic C-V measurements. High quality tungsten gate devices were obtained, even after annealing at temperatures as high as 650℃, which are sufficient for dopant activation in a self-aligned W gate CMOS fabrication process. Furthermore, effective barrier action of our LPCVD tungsten films against the penetration of copper, and its diffusion into the gate dielectric, in Cu/W gate devices at a temperature of 510℃ was demonstrated.