Dielectric and electrical characteristics of titanium-modified Ta2O5 thin films deposited on nitrided polysilicon by metalorganic chemical vapor deposition

Titanium-modified tantalum oxide thin films with a composition of (TaZO(5))(0.922)-(TiO2)(0.078), and pure Ta2O5 thin films of 12 nm thickness were prepared on a nitrided poly-Si electrode by liquid source delivery metalorganic chemical vapor deposition at 390 degrees C. The effective dielectric constant of the Ti-modified Ta2O5 thin films is higher than that of the pure Ta2O5 thin films whether they were crystallized or not. The highest value of the effective dielectric constant is 30.2 for the Ti-modified Ta2O5 thin films after being subjected to rapid thermal oxygen annealing (RTO) at 800 degrees C fur 30 s, but that of the pure Ta2O5 is only 22.4 under the same heat treatment conditions. Moreover, the former also has a high and stable insulating characteristic against bias voltage, i.e., a low leakage current of 1 x 10(-8) A/cm(2) can be maintained at 2.5 MV/cm after RTO at 850 degrees C for 90s, However, that of pure Ta2O5 only reaches 1 x 10(-7) A/cm(2) under the same treatment conditions. The relationship of current versus time (I-t) measured at room temperature also reveals the superior insulating property of Ti-modified Ta2O5 compared to that of pure Ta2O5 thin films. An excellent leakage current characteristic along with high capacitance suggests that the Ti-modified Ta2O5 thin film is a more promising material than the pure Ta2O5 film for use in the fabrication of capacitors for G-bit dynamic random access memories.