Charge trapping characteristics of HfYOx gate dielectrics on SiGe

Ultrathin HfYO_x gate dielectric has been deposited on Si_0.15Ge_0.85 by RF co-sputtering of HfO₂ and Y₂O₃ targets. HfYO_x layers were characterized by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray (EDX) and grazing incidence X-ray diffraction (GIXRD) to examine the composition and crystallinity. An atomic percentage of Hf:Y = 58.35:41.64 was achieved from the EDX analysis while GIXRD revealed a crystalline phase, if annealed above 500°C. Charge trapping/detrapping behavior of Al/HfYO_x/SiGe MIS capacitors have been studied under DC and AC voltage stressing with different amplitudes and dynamic voltage stresses in order to study the transient response. The degradation mechanism of the dielectric has also been studied. The current transients observed during dynamic voltage stress have been interpreted in terms of the charging/discharging of traps at SiGe/HfYO_x interface and bulk HfYO_x. The change in V_fb and gate current during unipolar pulse voltage stressing shows that the main degradation takes place at low frequencies.