Charge trapping characteristics of HfYOx gate dielectrics on SiGe

Ultrathin HfYO
_x
gate dielectric has been deposited on Si
_0.15
Ge
_0.85
by RF co-sputtering of HfO
₂
and Y
₂
O
₃
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.