Ef(1-x)Si(x)O(2) thin film was deposited on a Si substrate by low pressure chemical vapor deposition using the tetrakis-diethylamido-hafnium {Hf[N(C2H5)(2)](4)}/Tris-diethylamino-silane {SiH[N(C2H5)(2)](3))/O-2 gas system. During the HfO2 deposition, SiH[N(C2H5)](3) vapor was injected and Hf1-xSixO2 film was deposited. By increasing the amount of the supplied SiH[N(C2H5)(2)](3), the ratio of Si to Hf in the film increased and the refractive index of the film decreased. While the deposited HfO2 film was polycrystalline, Hf1-xSixO2 was amorphous. The step-coverage quality was slightly degraded as a result of the SiH[N(C2H5)(2)](3) injection. No residual C was detected in the film by XPS measurement indicating that the residual C amount was less than 1%. On the other hand, the amount of residual N increased with an increase in the supply of SiH[N(C2H5)(2)](3).