Ge-stabilized tetragonal ZrO2 as gate dielectric for Ge metal-oxide-semiconductor capacitors fabricated on Si substrate

A Ge-stabilized tetragonal ZrO2 (t-ZrO2) film formed by incorporating Ge atoms thermally driven from an underlying Ge layer into a ZrO2 film was investigated as the gate dielectric for Ge metal-oxide-semiconductor (MOS) capacitors fabricated on a Si substrate. A sole t-ZrO2 film on Ge is not eligible for the gate dielectric because of the poor interface quality. By using a thermally-grown ultrathin GeO2 film as an interfacial layer, the t-ZrO2/GeO2/Ge stack shows improved interface characteristics and a permittivity (κ) value of 36.6 for the t-ZrO2. In addition, the stack also demonstrates good leakage current since the amorphous GeO2 layer terminates grain boundary channels in the crystalline ZrO2. Further leakage current suppression can be achieved by a H2 annealing of the t-ZrO2/GeO2/Ge stack since the defects at grain boundaries can be effectively passivated, which makes a leakage current of 1.08×10−6 A/cm2 at VFB−1 V for effective oxide thickness of 1.66 nm and paves an alternative avenue to develop a high-performance crystalline gate dielectric for Ge MOS devices.