REDUCTION OF OXIDE CHARGE AND INTERFACE-TRAP DENSITY IN MOS CAPACITORS WITH ITO GATES

The electrical properties of MOS capacitors with an indium tin oxide (ITO) gate are studied in terms of the number density of the fixed oxide charge and of the interface traps N(f) and N(it), respectively. Both depend on the deposition conditions of ITO and the subsequent annealing procedures. The fixed oxide charge and the interface-trap density are minimized by depositing at a substrate temperature of 240-degrees-C at low power conditions and in an oxygen-rich ambient. Under these conditions, as-deposited ITO films are electrically conductive. The most effective annealing procedure consists of a two-step anneal: a 45-s rapid thermal anneal at 950-degrees-C in N2, followed by a 30-min anneal in N2/20% H-2 at 450-degrees-C. Typical values obtained for N(it), and N(f) are 4.2 X 10(10) cm-2 and 2.8 x 10(10) cm-2 , respectively. These values are further reduced to 1.9 X 10(10) cm-2 and less than or similar 5 X 10(9) cm-2, respectively, by depositing approximately 25-nm polycrystalline silicon on the gate insulation prior to the depositon of ITO.